title	Working with Digital Signature \| Syncfusion
description	This section explains how to create a digital signature in the PDF document by using Syncfusion .NET PDF library.
platform	document-processing
control	PDF
documentation	UG

Working with Digital Signature

To quickly get started with digitally signing a PDF document and validating signatures using the Blazor PDF Library, check this video: {% youtube "https://www.youtube.com/watch?v=NNIFh1Ckdzw&t=672s" %}

Adding a digital signature

The Essential^® PDF allows you to add a digital signature to the PDF document. To add a digital signature, you need a certificate with private keys. The Essential^® PDF provides support for digital signature by using the PFX files, Hardware Security Module (HSM), Online Certificate Status Protocol (OCSP), Certificate Revocation List (CRL), Windows Certificate Store, and supports signatures using the Elliptic Curve Digital Signature Algorithm (ECDSA).

The following code example explains how to add a digital signature to the PDF document by using PdfSignature class.

{% tabs %}

{% highlight c# tabtitle="C# [Cross-platform]" playgroundButtonLink="https://raw.githubusercontent.com/SyncfusionExamples/PDF-Examples/master/Digital%20Signature/Add-a-digital-signature-to-the-PDF-document/.NET/Add-a-digital-signature-to-the-PDF-document/Program.cs" %}

using Syncfusion.Drawing; using Syncfusion.Pdf; using Syncfusion.Pdf.Graphics; using Syncfusion.Pdf.Security;

//Creates a new PDF document. PdfDocument document = new PdfDocument(); //Adds a new page. PdfPageBase page = document.Pages.Add(); //Create PDF graphics for the page. PdfGraphics graphics = page.Graphics;

//Creates a certificate instance from PFX file with private key. FileStream certificateStream = new FileStream("PDF.pfx", FileMode.Open, FileAccess.Read); PdfCertificate pdfCert = new PdfCertificate(certificateStream, "password123"); //Creates a digital signature. PdfSignature signature = new PdfSignature(document, page, pdfCert, "Signature"); //Sets an image for signature field. FileStream imageStream = new FileStream("signature.jpg", FileMode.Open, FileAccess.Read); //Sets an image for signature field. PdfBitmap signatureImage = new PdfBitmap(imageStream); //Sets signature information. signature.Bounds = new RectangleF(new PointF(0, 0), signatureImage.PhysicalDimension); signature.SignedName = "Syncfusion"; signature.ContactInfo = "johndoe@owned.us"; signature.LocationInfo = "Honolulu, Hawaii"; signature.Reason = "I am author of this document."; //Draws the signature image. signature.Appearance.Normal.Graphics.DrawImage(signatureImage, 0, 0);

//Save the document document.Save("Output.pdf"); //Close the document. document.Close(true);

{% endhighlight %}

{% highlight c# tabtitle="C# [Windows-specific]" %}

using System.Drawing; using Syncfusion.Pdf; using Syncfusion.Pdf.Graphics; using Syncfusion.Pdf.Security;

//Creates a new PDF document PdfDocument document = new PdfDocument(); //Adds a new page PdfPageBase page = document.Pages.Add(); //Create PDF graphics for the page PdfGraphics graphics = page.Graphics;

//Saves and closes the document document.Save("Output.pdf"); document.Close(true);

{% endhighlight %}

{% highlight vb.net tabtitle="VB.NET [Windows-specific]" %}

Imports System.Drawing Imports Syncfusion.Pdf Imports Syncfusion.Pdf.Graphics Imports Syncfusion.Pdf.Security

'Creates a new PDF document Dim document As New PdfDocument() 'Adds a new page Dim page As PdfPageBase = document.Pages.Add() 'Create PDF graphics for the page Dim graphics As PdfGraphics = page.Graphics

'Creates a certificate instance from PFX file with private key Dim pdfCert As New PdfCertificate("PDF.pfx", "password123") 'Creates a digital signature Dim signature As New PdfSignature(document, page, pdfCert, "Signature") 'Sets an image for signature field Dim signatureImage As New PdfBitmap("signature.jpg") 'Sets signature information signature.Bounds = New RectangleF(New PointF(0, 0), signatureImage.PhysicalDimension) signature.SignedName = "Syncfusion" signature.ContactInfo = "johndoe@owned.us" signature.LocationInfo = "Honolulu, Hawaii" signature.Reason = "I am author of this document." 'Draws the signature image signature.Appearance.Normal.Graphics.DrawImage(signatureImage, 0, 0)

'Saves and closes the document document.Save("Output.pdf") document.Close(True)

{% endhighlight %}

{% endtabs %}

You can download a complete working sample from GitHub.

Adding a digital signature using stream

The following code example illustrates how to add a digital signature in the PDF document as stream using the PdfSignature class as follows.

{% tabs %}

using Syncfusion.Drawing; using Syncfusion.Pdf; using Syncfusion.Pdf.Graphics; using Syncfusion.Pdf.Security;

//Creates a certificate instance from PFX file with private key FileStream certificateStream = new FileStream("PDF.pfx", FileMode.Open, FileAccess.Read); PdfCertificate pdfCert = new PdfCertificate(certificateStream, "password123"); //Creates a digital signature PdfSignature signature = new PdfSignature(document, page, pdfCert, "Signature"); //Sets an image for signature field FileStream imageStream = new FileStream("signature.jpg", FileMode.Open, FileAccess.Read); //Sets an image for signature field PdfBitmap signatureImage = new PdfBitmap(imageStream); //Sets signature information signature.Bounds = new RectangleF(new PointF(0, 0), signatureImage.PhysicalDimension); signature.SignedName = "Syncfusion"; signature.ContactInfo = "johndoe@owned.us"; signature.LocationInfo = "Honolulu, Hawaii"; signature.Reason = "I am author of this document."; //Draws the signature image signature.Appearance.Normal.Graphics.DrawImage(signatureImage, 0, 0);

//Save the document document.Save("Output.pdf"); //Close the document. document.Close(true);

{% endhighlight %}

{% highlight c# tabtitle="C# [Windows-specific]" %}

using System.Drawing; using Syncfusion.Pdf; using Syncfusion.Pdf.Graphics; using Syncfusion.Pdf.Security;

//Gets a stream from .pfx file Stream pfxStream = File.OpenRead("PDF.pfx"); //Creates a certificate instance from PFX file stream with private key PdfCertificate pdfCert = new PdfCertificate(pfxStream, "password123"); //Creates a digital signature PdfSignature signature = new PdfSignature(document, page, pdfCert, "Signature"); //Sets an image for signature field PdfBitmap signatureImage = new PdfBitmap(@"signature.jpg"); //Sets signature information signature.Bounds = new RectangleF(new PointF(0, 0), signatureImage.PhysicalDimension); signature.SignedName = "Syncfusion"; signature.ContactInfo = "johndoe@owned.us"; signature.LocationInfo = "Honolulu, Hawaii"; signature.Reason = "I am author of this document."; //Draws the signature image signature.Appearance.Normal.Graphics.DrawImage(signatureImage, 0, 0);

//Saves and closes the document document.Save("Output.pdf"); document.Close(true);

{% endhighlight %}

{% highlight vb.net tabtitle="VB.NET [Windows-specific]" %}

Imports System.Drawing Imports Syncfusion.Pdf Imports Syncfusion.Pdf.Graphics Imports Syncfusion.Pdf.Security

'Gets stream from .pfx file Dim pfxStream As Stream = File.OpenRead("PDF.pfx") 'Creates a certificate instance from PFX file stream with private key Dim pdfCert As New PdfCertificate(pfxStream, "password123") 'Creates a digital signature Dim signature As New PdfSignature(document, page, pdfCert, "Signature") 'Sets an image for signature field Dim signatureImage As New PdfBitmap("signature.jpg") 'Sets signature information signature.Bounds = New RectangleF(New PointF(0, 0), signatureImage.PhysicalDimension) signature.SignedName = "Syncfusion" signature.ContactInfo = "johndoe@owned.us" signature.LocationInfo = "Honolulu, Hawaii" signature.Reason = "I am author of this document." 'Draws the signature image signature.Appearance.Normal.Graphics.DrawImage(signatureImage, 0, 0)

'Saves and closes the document document.Save("Output.pdf") document.Close(True)

{% endhighlight %}

{% endtabs %}

You can add a digital signature to an existing document as follows.

{% tabs %}

{% highlight c# tabtitle="C# [Cross-platform]" playgroundButtonLink="https://raw.githubusercontent.com/SyncfusionExamples/PDF-Examples/master/Digital%20Signature/Add-a-digital-signature-to-an-existing-document/.NET/Add-a-digital-signature-to-an-existing-document/Program.cs" %}

using Syncfusion.Drawing; using Syncfusion.Pdf; using Syncfusion.Pdf.Graphics; using Syncfusion.Pdf.Parsing; using Syncfusion.Pdf.Security;

//Load the PDF document PdfLoadedDocument loadedDocument = new PdfLoadedDocument("Input.pdf"); //Gets the page PdfLoadedPage page = loadedDocument.Pages[0] as PdfLoadedPage;

//Creates a signature field PdfSignatureField signatureField = new PdfSignatureField(page, "SignatureField"); signatureField.Bounds = new RectangleF(0, 0, 100, 100); signatureField.Signature = new PdfSignature(); //Adds certificate to the signature field FileStream certificateStream = new FileStream("PDF.pfx", FileMode.Open, FileAccess.Read); signatureField.Signature.Certificate = new PdfCertificate(certificateStream, "password123"); signatureField.Signature.Reason = "I am author of this document"; //Adds the field loadedDocument.Form.Fields.Add(signatureField);

//Save the document loadedDocument.Save("Output.pdf"); //Close the document. loadedDocument.Close(true);

{% endhighlight %}

{% highlight c# tabtitle="C# [Windows-specific]" %}

using System.Drawing; using Syncfusion.Pdf; using Syncfusion.Pdf.Graphics; using Syncfusion.Pdf.Parsing; using Syncfusion.Pdf.Security;

//Loads the PDF document with signature field PdfLoadedDocument loadedDocument = new PdfLoadedDocument("Input.pdf");
//Gets the page PdfLoadedPage page = loadedDocument.Pages[0] as PdfLoadedPage;

//Creates a signature field PdfSignatureField signatureField = new PdfSignatureField(page, "SignatureField"); signatureField.Bounds = new RectangleF(0, 0, 100, 100); signatureField.Signature = new PdfSignature(); //Adds certificate to the signature field signatureField.Signature.Certificate = new PdfCertificate(@"PDF.pfx", "password123"); signatureField.Signature.Reason = "I am author of this document"; //Adds the field loadedDocument.Form.Fields.Add(signatureField);

//Saves the certified PDF document loadedDocument.Save(@"Output.pdf"); loadedDocument.Close(true);

{% endhighlight %}

{% highlight vb.net tabtitle="VB.NET [Windows-specific]" %}

Imports System.Drawing Imports Syncfusion.Pdf Imports Syncfusion.Pdf.Graphics Imports Syncfusion.Pdf.Parsing Imports Syncfusion.Pdf.Security

'Loads the PDF document with signature field Dim loadedDocument As New PdfLoadedDocument("Input.pdf") 'Gets the page Dim page As PdfLoadedPage = TryCast(loadedDocument.Pages(0), PdfLoadedPage)

'Creates a signature field Dim signatureField As New PdfSignatureField(page, "SignatureField") signatureField.Bounds = New RectangleF(0, 0, 100, 100) signatureField.Signature = New PdfSignature() 'Adds certificate to the signature field signatureField.Signature.Certificate = New PdfCertificate("PDF.pfx", "password123") signatureField.Signature.Reason = "I am author of this document" 'Adds the field loadedDocument.Form.Fields.Add(signatureField)

'Saves the certified PDF document loadedDocument.Save("Output.pdf") loadedDocument.Close(True)

{% endhighlight %}

{% endtabs %}

You can download a complete working sample from GitHub.

Adding a digital signature using X509Certificate2

The following code example illustrates how to add digital signature in a PDF document using X509Certificate2 as follows.

{% tabs %}

{% highlight c# tabtitle="C# [Cross-platform]" playgroundButtonLink="https://raw.githubusercontent.com/SyncfusionExamples/PDF-Examples/master/Digital%20Signature/Add-digital-signature-using-X509Certificate2/.NET/Add-digital-signature-using-X509Certificate2/Program.cs" %}

using Syncfusion.Drawing; using Syncfusion.Pdf; using Syncfusion.Pdf.Graphics; using Syncfusion.Pdf.Security; using System.Security.Cryptography.X509Certificates;

//Creates a new PDF document PdfDocument document = new PdfDocument(); //Adds a new page
PdfPage page = document.Pages.Add(); //Create PDF graphics for the page PdfGraphics graphics = page.Graphics;

//Creates a certificate instance from PFX file with private key
X509Certificate2 certificate = new X509Certificate2("PDF.pfx", "password123"); PdfCertificate pdfCertificate = new PdfCertificate(certificate); //Creates a digital signature
PdfSignature signature = new PdfSignature(document, page, pdfCertificate, "Signature"); //Sets an image for signature field FileStream imageStream = new FileStream("signature.jpg", FileMode.Open, FileAccess.Read); PdfBitmap signatureImage = new PdfBitmap(imageStream); //Sets signature information signature.Bounds = new RectangleF(new PointF(0, 0), signatureImage.PhysicalDimension); signature.SignedName = "Syncfusion"; signature.ContactInfo = "johndoe@owned.us"; signature.LocationInfo = "Honolulu, Hawaii"; signature.Reason = "I am author of this document."; //Draws the signature image signature.Appearance.Normal.Graphics.DrawImage(signatureImage, 0, 0);

//Save the document document.Save("Output.pdf"); //Close the document. document.Close(true);

{% endhighlight %}

{% highlight c# tabtitle="C# [Windows-specific]" %}

using System.Drawing; using Syncfusion.Pdf; using Syncfusion.Pdf.Graphics; using Syncfusion.Pdf.Security; using System.Security.Cryptography.X509Certificates;

//Creates a new PDF document PdfDocument document = new PdfDocument(); //Adds a new page
PdfPage page = document.Pages.Add(); //Create PDF graphics for the page PdfGraphics graphics = page.Graphics;

//Creates a certificate instance from PFX file with private key
X509Certificate2 certificate = new X509Certificate2("PDF.pfx", "password123"); PdfCertificate pdfCertificate = new PdfCertificate(certificate); //Creates a digital signature
PdfSignature signature = new PdfSignature(document, page, pdfCertificate, "Signature"); //Sets an image for signature field PdfBitmap signatureImage = new PdfBitmap(@"signature.jpg"); //Sets signature information signature.Bounds = new RectangleF(new PointF(0, 0), signatureImage.PhysicalDimension); signature.SignedName = "Syncfusion"; signature.ContactInfo = "johndoe@owned.us"; signature.LocationInfo = "Honolulu, Hawaii"; signature.Reason = "I am author of this document."; //Draws the signature image signature.Appearance.Normal.Graphics.DrawImage(signatureImage, 0, 0);

//Save the document document.Save("Output.pdf"); //Close the document document.Close(true);

{% endhighlight %}

{% highlight vb.net tabtitle="VB.NET [Windows-specific]" %}

Imports Syncfusion.Drawing Imports Syncfusion.Pdf Imports Syncfusion.Pdf.Graphics Imports Syncfusion.Pdf.Security Imports System.Security.Cryptography.X509Certificates

'Creates a new PDF document Dim document As New PdfDocument() 'Adds a new page
Dim page As PdfPage = document.Pages.Add() 'Create PDF graphics for the page Dim graphics As PdfGraphics = page.Graphics

'Creates a certificate instance from PFX file with private key
Dim certificate As New X509Certificate2("PDF.pfx", "password123") Dim pdfCertificate As New PdfCertificate(certificate) 'Creates a digital signature Dim signature As New PdfSignature(document, page, pdfCertificate, "Signature") 'Sets an image for signature field Dim signatureImage As New PdfBitmap("signature.jpg") 'Sets signature information signature.Bounds = New RectangleF(New PointF(0, 0), signatureImage.PhysicalDimension) signature.SignedName = "Syncfusion" signature.ContactInfo = "johndoe@owned.us" signature.LocationInfo = "Honolulu, Hawaii" signature.Reason = "I am author of this document." 'Draws the signature image signature.Appearance.Normal.Graphics.DrawImage(signatureImage, 0, 0)

'Save the document document.Save("Output.pdf") 'Close the document document.Close(True)

{% endhighlight %}

{% endtabs %}

You can download a complete working sample from GitHub.

Signing an existing document

You can load the signature field from the existing PDF document using PdfLoadedSignatureField class and add certificate to the document using PdfCertificate class.

{% tabs %}

{% highlight c# tabtitle="C# [Cross-platform]" playgroundButtonLink="https://raw.githubusercontent.com/SyncfusionExamples/PDF-Examples/master/Digital%20Signature/Signing-an-existing-PDF-document/.NET/Signing-an-existing-PDF-document/Program.cs" %}

using Syncfusion.Pdf; using Syncfusion.Pdf.Parsing; using Syncfusion.Pdf.Security;

//Load the PDF document PdfLoadedDocument loadedDocument = new PdfLoadedDocument("Input.pdf"); //Gets the first page of the document PdfLoadedPage page = loadedDocument.Pages[0] as PdfLoadedPage; //Gets the first signature field of the PDF document PdfLoadedSignatureField field = loadedDocument.Form.Fields[0] as PdfLoadedSignatureField;

//Creates a certificate FileStream certificateStream = new FileStream("PDF.pfx", FileMode.Open, FileAccess.Read); PdfCertificate certificate = new PdfCertificate(certificateStream, "password123"); field.Signature = new PdfSignature(loadedDocument, page, certificate, "Signature", field);

//Save the document loadedDocument.Save("Output.pdf"); //Close the document. loadedDocument.Close(true);

{% endhighlight %}

{% highlight c# tabtitle="C# [Windows-specific]" %}

using Syncfusion.Pdf; using Syncfusion.Pdf.Parsing; using Syncfusion.Pdf.Security;

//Loads a PDF document PdfLoadedDocument loadedDocument = new PdfLoadedDocument("Input.pdf"); //Gets the first page of the document PdfLoadedPage page = loadedDocument.Pages[0] as PdfLoadedPage; //Gets the first signature field of the PDF document PdfLoadedSignatureField field = loadedDocument.Form.Fields[0] as PdfLoadedSignatureField;

//Creates a certificate PdfCertificate certificate = new PdfCertificate(@"PDF.pfx", "password123"); field.Signature = new PdfSignature(loadedDocument,page,certificate,"Signature",field);

//Saves the document loadedDocument.Save("Output.pdf"); //Close the document loadedDocument.Close(true);

{% endhighlight %}

{% highlight vb.net tabtitle="VB.NET [Windows-specific]" %}

Imports Syncfusion.Pdf Imports Syncfusion.Pdf.Parsing Imports Syncfusion.Pdf.Security

'Loads a PDF document Dim loadedDocument As New PdfLoadedDocument("Input.pdf") 'Gets the first page of the document Dim page As PdfLoadedPage = TryCast(loadedDocument.Pages(0), PdfLoadedPage) 'Gets the first signature field of the PDF document Dim field As PdfLoadedSignatureField = TryCast(loadedDocument.Form.Fields(0), PdfLoadedSignatureField)

'Creates a certificate Dim certificate As New PdfCertificate("PDF.pfx", "password123") field.Signature = New PdfSignature(loadedDocument, page, certificate, "Signature", field)

'Saves the document loadedDocument.Save("Output.pdf") 'Close the document loadedDocument.Close(True)

{% endhighlight %}

{% endtabs %}

You can download a complete working sample from GitHub.

Sign an existing document using stream

You can load the signature field from an existing PDF document using PdfLoadedSignatureField class and add certificate to the document as stream using PdfCertificate as follows.

{% tabs %}

{% highlight c# tabtitle="C# [Cross-platform]" %}

using Syncfusion.Pdf; using Syncfusion.Pdf.Parsing; using Syncfusion.Pdf.Security;

//Save the document loadedDocument.Save("Output.pdf"); //Close the document. loadedDocument.Close(true);

{% endhighlight %}

{% highlight c# tabtitle="C# [Windows-specific]" %}

using Syncfusion.Pdf; using Syncfusion.Pdf.Parsing; using Syncfusion.Pdf.Security;

//Gets the stream from .pfx file Stream pfxStream = File.OpenRead("PDF.pfx"); //Creates a certificate instance from PFX file stream with private key PdfCertificate certificate = new PdfCertificate(pfxStream, "password123"); field.Signature = new PdfSignature(loadedDocument, page, certificate, "Signature", field);

//Save the document loadedDocument.Save("Output.pdf"); //Close the document loadedDocument.Close(true);

{% endhighlight %}

{% highlight vb.net tabtitle="VB.NET [Windows-specific]" %}

Imports Syncfusion.Pdf Imports Syncfusion.Pdf.Parsing Imports Syncfusion.Pdf.Security

'Gets the stream from .pfx file Dim pfxStream As Stream = File.OpenRead("PDF.pfx") 'Creates a certificate instance from PFX file stream with private key Dim certificate As New PdfCertificate(pfxStream, "password123") field.Signature = New PdfSignature(loadedDocument, page, certificate, "Signature", field)

'Save the document loadedDocument.Save("Output.pdf") 'Close the document loadedDocument.Close(True)

{% endhighlight %}

{% endtabs %}

Verify if a signature field is signed

The IsSigned property in the PdfLoadedSignatureField class allows you to determine whether a signature field in a PDF document has been signed.

The following code example demonstrates how to check if a signature field is signed.

{% tabs %}

{% highlight c# tabtitle="C# [Cross-platform]" playgroundButtonLink="https://raw.githubusercontent.com/SyncfusionExamples/PDF-Examples/master/Digital%20Signature/Check-If-PDF-Is-Signed/.NET/Check-If-PDF-Is-Signed/Program.cs" %}

using Syncfusion.Pdf.Parsing;

// Load the PDF document PdfLoadedDocument loadedDocument = new PdfLoadedDocument("Input.pdf");

// Check if the document contains a form with fields if (loadedDocument.Form == null || loadedDocument.Form.Fields.Count == 0) { Console.WriteLine("No signature fields found in the document."); } else { // Iterate through all fields in the form foreach (PdfLoadedField field in loadedDocument.Form.Fields) { // Check if the field is a signature field PdfLoadedSignatureField signatureField = field as PdfLoadedSignatureField; if (signatureField != null) { // Determine whether the signature field is signed or not string status = signatureField.IsSigned ? "Signed" : "UnSigned";

        // Output the result for each signature field
        Console.WriteLine("Signature Field " + signatureField.Name + " is: " + status);
    }
}

}

// Close the document loadedDocument.Close(true);

{% endhighlight %}

{% highlight c# tabtitle="C# [Windows-specific]" %}

using Syncfusion.Pdf.Parsing;

// Load the PDF document PdfLoadedDocument loadedDocument = new PdfLoadedDocument("Input.pdf");

        // Output the result for each signature field
        Console.WriteLine("Signature Field " + signatureField.Name + " is: " + status);
    }
}

}

// Close the document loadedDocument.Close(true);

{% endhighlight %}

{% highlight vb.net tabtitle="VB.NET [Windows-specific]" %}

Imports Syncfusion.Pdf.Parsing

' Load the PDF document Dim loadedDocument As New PdfLoadedDocument("Input.pdf")

' Check if the document contains a form with fields If loadedDocument.Form Is Nothing OrElse loadedDocument.Form.Fields.Count = 0 Then Console.WriteLine("No signature fields found in the document.") Else ' Iterate through all fields in the form For Each field As PdfLoadedField In loadedDocument.Form.Fields ' Check if the field is a signature field Dim signatureField As PdfLoadedSignatureField = TryCast(field, PdfLoadedSignatureField) If signatureField IsNot Nothing Then ' Determine whether the signature field is signed or not Dim status As String = If(signatureField.IsSigned, "Signed", "UnSigned")

        ' Output the result for each signature field
        Console.WriteLine("Signature Field " & signatureField.Name & " is: " & status)
    End If
Next

End If

' Close the document loadedDocument.Close(True)

{% endhighlight %}

{% endtabs %}

You can download a complete working sample from GitHub.

Externally sign a PDF document

You can sign the PDF document with an external digital signature created from various sources, such as an HSM, USB token, smart card, or other cloud services such as DigitalSign. The following approaches are available for externally signing the PDF documents.

ComputeHash event
IPdfExternalSigner interface

Externally sign the PDF document using ComputeHash event

The following code example shows how to sign the PDF document from an external signature using ComputeHash event.

{% tabs %}

{% highlight c# tabtitle="C# [Cross-platform]" playgroundButtonLink="https://raw.githubusercontent.com/SyncfusionExamples/PDF-Examples/master/Digital%20Signature/Externally-sign-a-PDF-document/.NET/Externally-sign-a-PDF-document/Program.cs" %}

using Syncfusion.Pdf.Parsing; using Syncfusion.Pdf.Security; using System.Security.Cryptography; using System.Security.Cryptography.Pkcs; using System.Security.Cryptography.X509Certificates;

//Load the PDF document PdfLoadedDocument document = new PdfLoadedDocument("Input.pdf");

//Creates a digital signature PdfSignature signature = new PdfSignature(document, document.Pages[0], null, "DigitalSignature"); signature.ComputeHash += Signature_ComputeHash;

//Save the document document.Save("Output.pdf"); //Close the document. document.Close(true);

private static void Signature_ComputeHash1(object sender, PdfSignatureEventArgs ars) { //Get the document bytes byte[] documentBytes = ars.Data; SignedCms signedCms = new SignedCms(new ContentInfo(documentBytes), detached: true);

//Compute the signature using the specified digital ID file and the password
FileStream certificateStream = new FileStream("DigitalSignatureTest.pfx", FileMode.Open, FileAccess.Read);
X509Certificate2 certificate = new X509Certificate2(certificateStream, "DigitalPass123");
var cmsSigner = new CmsSigner(certificate);

//Set the digest algorithm SHA256
cmsSigner.DigestAlgorithm = new Oid("2.16.840.1.101.3.4.2.1");
signedCms.ComputeSignature(cmsSigner);

//Embed the encoded digital signature to the PDF document
ars.SignedData = signedCms.Encode();

}

{% endhighlight %}

{% highlight c# tabtitle="C# [Windows-specific]" %}

using Syncfusion.Pdf.Parsing; using Syncfusion.Pdf.Security; using System.Security.Cryptography; using System.Security.Cryptography.Pkcs; using System.Security.Cryptography.X509Certificates;

//Load existing PDF document PdfLoadedDocument document = new PdfLoadedDocument("PDF_Succinctly.pdf"); //Creates a digital signature PdfSignature signature = new PdfSignature(document, document.Pages[0], null, "DigitalSignature"); signature.ComputeHash += Signature_ComputeHash;

//Save the PDF document document.Save("ExternalSignature.pdf"); //Close the document document.Close(true);

void Signature_ComputeHash(object sender, PdfSignatureEventArgs arguments) { //Get the document bytes byte[] documentBytes = arguments.Data; SignedCms signedCms = new SignedCms(new ContentInfo(documentBytes), detached: true);

//Compute the signature using the specified digital ID file and the password
X509Certificate2 certificate = new X509Certificate2("DigitalSignatureTest.pfx", "DigitalPass123");
var cmsSigner = new CmsSigner(certificate);

//Set the digest algorithm SHA256
cmsSigner.DigestAlgorithm = new Oid("2.16.840.1.101.3.4.2.1");
signedCms.ComputeSignature(cmsSigner);

//Embed the encoded digital signature to the PDF document
arguments.SignedData = signedCms.Encode();

}

{% endhighlight %}

{% highlight vb.net tabtitle="VB.NET [Windows-specific]" %}

Imports Syncfusion.Pdf.Parsing Imports Syncfusion.Pdf.Security Imports System.Security.Cryptography Imports System.Security.Cryptography.Pkcs Imports System.Security.Cryptography.X509Certificates

'Load existing PDF document Dim document As PdfLoadedDocument = New PdfLoadedDocument("PDF_Succinctly.pdf") 'Creates a digital signature Dim signature As PdfSignature = New PdfSignature(document, document.Pages(0), Nothing, "DigitalSignature") AddHandler signature.ComputeHash, AddressOf Signature_ComputeHash

'Save the PDF document document.Save("ExternalSignature.pdf") 'Close the document document.Close(True)

Private Sub Signature_ComputeHash(ByVal sender As Object, ByVal arguments As PdfSignatureEventArgs) 'Get the document bytes Dim documentBytes As Byte() = arguments.Data Dim signedCms As SignedCms = New SignedCms(New ContentInfo(documentBytes), detached:=True)

'Compute the signature using the specified digital ID file and the password
Dim certificate As X509Certificate2 = New X509Certificate2("DigitalSignatureTest.pfx", "DigitalPass123")
Dim cmsSigner = New CmsSigner(certificate)

'Set the digest algorithm SHA256
cmsSigner.DigestAlgorithm = New Oid("2.16.840.1.101.3.4.2.1")
signedCms.ComputeSignature(cmsSigner)

'Embed the encoded digital signature to the PDF document
arguments.SignedData = signedCms.Encode()

End Sub

{% endhighlight %}

{% endtabs %}

You can download a complete working sample from GitHub.

Externally sign the PDF document using IPdfExternalSigner

The following code example shows how to sign the PDF document from external signature using IPdfExternalSigner.

{% tabs %}

{% highlight c# tabtitle="C# [Cross-platform]" playgroundButtonLink="https://raw.githubusercontent.com/SyncfusionExamples/PDF-Examples/master/Digital%20Signature/Externally-sign-the-PDF-document-using-IPdfExternalSigner/.NET/Externally-sign-the-PDF-document/Program.cs" %}

using Syncfusion.Pdf.Parsing; using Syncfusion.Pdf.Security; using Syncfusion.Drawing; using System.Security.Cryptography.X509Certificates; using System.Security.Cryptography;

//Load the PDF document PdfLoadedDocument loadedDocument = new PdfLoadedDocument("Input.pdf");

//Creates a digital signature. PdfSignature signature = new PdfSignature(loadedDocument, loadedDocument.Pages[0], null, "Signature"); //Sets the signature information. signature.Bounds = new RectangleF(new PointF(0, 0), new SizeF(100, 30)); signature.Settings.CryptographicStandard = CryptographicStandard.CADES; signature.Settings.DigestAlgorithm = DigestAlgorithm.SHA1;

//Create an external signer. IPdfExternalSigner externalSignature = new ExternalSigner("SHA1");

//Add public certificates. List certificates = new List(); certificates.Add(new X509Certificate2(Convert.FromBase64String(PublicCert))); signature.AddExternalSigner(externalSignature, certificates, null);

//Save the document loadedDocument.Save("Output.pdf"); //Close the document. loadedDocument.Close(true);

//Create the external signer class and sign the document hash. class ExternalSigner : IPdfExternalSigner { private string _hashAlgorithm; public string HashAlgorithm { get { return _hashAlgorithm; } }

public ExternalSigner(string hashAlgorithm)
{
    _hashAlgorithm = hashAlgorithm;
}
public byte[] Sign(byte[] message, out byte[] timeStampResponse)
{
    timeStampResponse = null;
    FileStream certificateStream = new FileStream("PDF.pfx", FileMode.Open, FileAccess.Read);
    X509Certificate2 digitalID = new X509Certificate2(new X509Certificate2(certificateStream, "password123"));
    if (digitalID.PrivateKey is System.Security.Cryptography.RSACryptoServiceProvider)
    {
        System.Security.Cryptography.RSACryptoServiceProvider rsa = (System.Security.Cryptography.RSACryptoServiceProvider)digitalID.PrivateKey;
        return rsa.SignData(message, HashAlgorithm);
    }
    else if (digitalID.PrivateKey is RSACng)
    {
        RSACng rsa = (RSACng)digitalID.PrivateKey;
        return rsa.SignData(message, System.Security.Cryptography.HashAlgorithmName.SHA1, RSASignaturePadding.Pkcs1);
    }
    else if (digitalID.PrivateKey is System.Security.Cryptography.RSAOpenSsl)
    {       
        System.Security.Cryptography.RSAOpenSsl rsa = (System.Security.Cryptography.RSAOpenSsl)digitalID.PrivateKey;
        return rsa.SignData(message, System.Security.Cryptography.HashAlgorithmName.SHA1, RSASignaturePadding.Pkcs1);
       }
    return null;
}

}

{% endhighlight %}

{% highlight c# tabtitle="C# [Windows-specific]" %}

using Syncfusion.Pdf.Parsing; using Syncfusion.Pdf.Security; using System.Drawing; using System.Security.Cryptography.X509Certificates; using System.Security.Cryptography;

//Load an existing PDF document. PdfLoadedDocument loadedDocument = new PdfLoadedDocument("Input.pdf");

//Create an external signer. IPdfExternalSigner externalSignature = new ExternalSigner("SHA1");

//Saves the document. loadedDocument.Save("Output.pdf"); //Closes the document. loadedDocument.Close(true);

public ExternalSigner(string hashAlgorithm)
{
    _hashAlgorithm = hashAlgorithm;
}
public byte[] Sign(byte[] message, out byte[] timeStampResponse)
{
    timeStampResponse = null;

    X509Certificate2 digitalID = new X509Certificate2(new X509Certificate2(Path.GetFullPath("PDF.pfx"), "password123"));
    if (digitalID.PrivateKey is System.Security.Cryptography.RSACryptoServiceProvider)
    {
        System.Security.Cryptography.RSACryptoServiceProvider rsa = (System.Security.Cryptography.RSACryptoServiceProvider)digitalID.PrivateKey;
        return rsa.SignData(message, HashAlgorithm);
    }
    else if (digitalID.PrivateKey is RSACng)
    {
        RSACng rsa = (RSACng)digitalID.PrivateKey;
        return rsa.SignData(message, System.Security.Cryptography.HashAlgorithmName.SHA1, RSASignaturePadding.Pkcs1);
    }
    return null;
}

}

{% endhighlight %}

{% highlight vb.net tabtitle="VB.NET [Windows-specific]" %}

Imports Syncfusion.Pdf.Parsing Imports Syncfusion.Pdf.Security Imports System.Security.Cryptography Imports System.Drawing Imports System.Security.Cryptography.X509Certificates

'Load an existing PDF document. Dim loadedDocument As PdfLoadedDocument = New PdfLoadedDocument("Input.pdf")

'Creates a digital signature. Dim signature As PdfSignature = New PdfSignature(loadedDocument, loadedDocument.Pages(0), Nothing, "Signature") 'Sets the signature information. signature.Bounds = New RectangleF(New PointF(0, 0), New SizeF(100, 30)) signature.Settings.CryptographicStandard = CryptographicStandard.CADES signature.Settings.DigestAlgorithm = DigestAlgorithm.SHA1

'Create an external signer. Dim externalSignature As IPdfExternalSigner = New ExternalSigner("SHA1") Dim certificates As List(Of X509Certificate2) = New List(Of X509Certificate2)() certificates.Add(New X509Certificate2(Convert.FromBase64String(PublicCert))) signature.AddExternalSigner(externalSignature, certificates, Nothing)

'Saves the document. loadedDocument.Save("Output.pdf") 'Closes the document. loadedDocument.Close(True)

Class ExternalSigner Implements IPdfExternalSigner

Private _hashAlgorithm As String

Public ReadOnly Property HashAlgorithm As String Implements IPdfExternalSigner.HashAlgorithm
    Get
        Return _hashAlgorithm
    End Get
End Property

Public Sub New(ByVal hashAlgorithm As String)
    _hashAlgorithm = hashAlgorithm
End Sub

Public Function Sign(message() As Byte, ByRef timeStampResponse() As Byte) As Byte() Implements IPdfExternalSigner.Sign
    timeStampResponse = Nothing
    Dim digitalID As X509Certificate2 = New X509Certificate2(New X509Certificate2("PDF.pfx", "password123"))

    If TypeOf digitalID.PrivateKey Is System.Security.Cryptography.RSACryptoServiceProvider Then
        Dim rsa As System.Security.Cryptography.RSACryptoServiceProvider = CType(digitalID.PrivateKey, System.Security.Cryptography.RSACryptoServiceProvider)
        Return rsa.SignData(message, HashAlgorithm)
    ElseIf TypeOf digitalID.PrivateKey Is RSACng Then
        Dim rsa As RSACng = CType(digitalID.PrivateKey, RSACng)
        Return rsa.SignData(message, System.Security.Cryptography.HashAlgorithmName.SHA1, RSASignaturePadding.Pkcs1)
    End If

    Return Nothing
End Function

End Class

{% endhighlight %}

{% endtabs %}

You can download a complete working sample from GitHub.

Adding Timestamps to a PDF document using external signing

This section explains how to add a timestamp to a PDF document during the external signing process. We have implemented a solution that generates a timestamp response from a timestamp server URI using the BouncyCastle library. The accepted timestamp token follows the RFC3161 standard.

N> In this example, we have used the open-source BouncyCastle library. Ensure you review its licensing before including it in your production environment. Alternatively, you can directly use the timestamp token provided by your service provider.

The following example illustrates the process of adding timestamps to a PDF document during the external signing process.

{% tabs %}

{% highlight c# tabtitle="C# [Cross-platform]" %}

using Syncfusion.Pdf.Parsing; using Syncfusion.Pdf.Security; using Syncfusion.Drawing; using System.Security.Cryptography.X509Certificates; using System.Security.Cryptography; using Org.BouncyCastle.Tsp; using System.Net; using System.Text; using Org.BouncyCastle.Math;

//Load the PDF document PdfLoadedDocument loadedDocument = new PdfLoadedDocument("Input.pdf");

// Create a digital signature for the first page of the document. PdfSignature signature = new PdfSignature(loadedDocument, loadedDocument.Pages[0], null, "Signature");

// Set the signature bounds and cryptographic settings. signature.Bounds = new RectangleF(new PointF(0, 0), new SizeF(100, 30)); signature.Settings.CryptographicStandard = CryptographicStandard.CADES; signature.Settings.DigestAlgorithm = DigestAlgorithm.SHA1;

// Create an external signer using the SHA1 hash algorithm. IPdfExternalSigner externalSignature = new ExternalSigner("SHA1");

// Add the public certificates for the external signer. List certificates = new List(); certificates.Add(new X509Certificate2(Convert.FromBase64String(PublicCert))); signature.AddExternalSigner(externalSignature, certificates, null);

//Save the document loadedDocument.Save("Output.pdf"); //Close the document. loadedDocument.Close(true);

{% endhighlight %}

{% highlight c# tabtitle="C# [Windows-specific]" %}

//Load an existing PDF document. PdfLoadedDocument loadedDocument = new PdfLoadedDocument("Input.pdf");

//Create an external signer. IPdfExternalSigner externalSignature = new ExternalSigner("SHA1");

//Saves the document. loadedDocument.Save("Output.pdf"); //Closes the document. loadedDocument.Close(true);

{% endhighlight %}

{% highlight vb.net tabtitle="VB.NET [Windows-specific]" %}

Imports Syncfusion.Pdf.Parsing Imports Syncfusion.Pdf.Security Imports Syncfusion.Drawing Imports System.Security.Cryptography.X509Certificates Imports System.Security.Cryptography Imports Org.BouncyCastle.Tsp Imports System.Net Imports System.Text Imports Org.BouncyCastle.Math

'Load an existing PDF document. Dim loadedDocument As PdfLoadedDocument = New PdfLoadedDocument("Input.pdf")

'Saves the document. loadedDocument.Save("Output.pdf") 'Closes the document. loadedDocument.Close(True)

{% endhighlight %}

{% endtabs %}

To sign the document using the X509Certificate2 API and generate an RFC3161-compliant timestamp token with the BouncyCastle library, add the following code:

{% tabs %}

{% highlight c# tabtitle="C# [Cross-platform]" %}

// External signer class that implements IPdfExternalSigner for signing the document hash. class ExternalSigner : IPdfExternalSigner { private string _hashAlgorithm;

// Gets the hash algorithm used for signing. public string HashAlgorithm { get { return _hashAlgorithm; } }

// Constructor that sets the hash algorithm for the signer. public ExternalSigner(string hashAlgorithm) { _hashAlgorithm = hashAlgorithm; }

// Sign the document hash and return the timestamp response. public byte[] Sign(byte[] message, out byte[] timeStampResponse) { byte[] signedBytes = null; X509Certificate2 digitalID = new X509Certificate2(new X509Certificate2(Path.GetFullPath(@"Data/PDF.pfx"), "password123"));

  // Use the appropriate signing algorithm based on the private key type.
  if (digitalID.PrivateKey is System.Security.Cryptography.RSACryptoServiceProvider)
  {
      System.Security.Cryptography.RSACryptoServiceProvider rsa = (System.Security.Cryptography.RSACryptoServiceProvider)digitalID.PrivateKey;
      signedBytes = rsa.SignData(message, HashAlgorithm);
  }
  else if (digitalID.PrivateKey is RSACng)
  {
      RSACng rsa = (RSACng)digitalID.PrivateKey;
      signedBytes = rsa.SignData(message, System.Security.Cryptography.HashAlgorithmName.SHA1, RSASignaturePadding.Pkcs1);
  }

  // Generate an RFC3161 timestamp token for the signed data.
  timeStampResponse = GetRFC3161TimeStampToken(signedBytes);
  return signedBytes;

}

// Generate the RFC3161 timestamp token using the provided signed data. public byte[] GetRFC3161TimeStampToken(byte[] bytes) { SHA1 sha1 = SHA1CryptoServiceProvider.Create(); byte[] hash = sha1.ComputeHash(bytes);

  // Create a timestamp request using the SHA1 hash.
  TimeStampRequestGenerator reqGen = new TimeStampRequestGenerator();
  reqGen.SetCertReq(true);
  TimeStampRequest tsReq = reqGen.Generate(TspAlgorithms.Sha1, hash, BigInteger.ValueOf(100));
  byte[] tsData = tsReq.GetEncoded();

  // Send the timestamp request to the server.
  HttpWebRequest req = (HttpWebRequest)WebRequest.Create("https://rfc3161.ai.moda"); // Update your timestamp URI here
  req.Method = "POST";
  req.ContentType = "application/timestamp-query";
  req.Headers.Add("Authorization", "Basic " + Convert.ToBase64String(Encoding.ASCII.GetBytes("9024:yourPass")));
  req.ContentLength = tsData.Length;

  // Write the request data to the stream.
  Stream reqStream = req.GetRequestStream();
  reqStream.Write(tsData, 0, tsData.Length);
  reqStream.Close();

  // Get the timestamp response from the server.
  HttpWebResponse res = (HttpWebResponse)req.GetResponse();
  if (res != null)
  {
      Stream resStream = new BufferedStream(res.GetResponseStream());
      TimeStampResponse tsRes = new TimeStampResponse(resStream);
      return tsRes.TimeStampToken.GetEncoded();
  }

  return null;

} }

{% endhighlight %}

{% highlight c# tabtitle="C# [Windows-specific]" %}

// External signer class that implements IPdfExternalSigner for signing the document hash. class ExternalSigner : IPdfExternalSigner { private string _hashAlgorithm;

// Gets the hash algorithm used for signing. public string HashAlgorithm { get { return _hashAlgorithm; } }

// Constructor that sets the hash algorithm for the signer. public ExternalSigner(string hashAlgorithm) { _hashAlgorithm = hashAlgorithm; }

  // Use the appropriate signing algorithm based on the private key type.
  if (digitalID.PrivateKey is System.Security.Cryptography.RSACryptoServiceProvider)
  {
      System.Security.Cryptography.RSACryptoServiceProvider rsa = (System.Security.Cryptography.RSACryptoServiceProvider)digitalID.PrivateKey;
      signedBytes = rsa.SignData(message, HashAlgorithm);
  }
  else if (digitalID.PrivateKey is RSACng)
  {
      RSACng rsa = (RSACng)digitalID.PrivateKey;
      signedBytes = rsa.SignData(message, System.Security.Cryptography.HashAlgorithmName.SHA1, RSASignaturePadding.Pkcs1);
  }

  // Generate an RFC3161 timestamp token for the signed data.
  timeStampResponse = GetRFC3161TimeStampToken(signedBytes);
  return signedBytes;

}

  // Create a timestamp request using the SHA1 hash.
  TimeStampRequestGenerator reqGen = new TimeStampRequestGenerator();
  reqGen.SetCertReq(true);
  TimeStampRequest tsReq = reqGen.Generate(TspAlgorithms.Sha1, hash, BigInteger.ValueOf(100));
  byte[] tsData = tsReq.GetEncoded();

  // Send the timestamp request to the server.
  HttpWebRequest req = (HttpWebRequest)WebRequest.Create("https://rfc3161.ai.moda"); // Update your timestamp URI here
  req.Method = "POST";
  req.ContentType = "application/timestamp-query";
  req.Headers.Add("Authorization", "Basic " + Convert.ToBase64String(Encoding.ASCII.GetBytes("9024:yourPass")));
  req.ContentLength = tsData.Length;

  // Write the request data to the stream.
  Stream reqStream = req.GetRequestStream();
  reqStream.Write(tsData, 0, tsData.Length);
  reqStream.Close();

  // Get the timestamp response from the server.
  HttpWebResponse res = (HttpWebResponse)req.GetResponse();
  if (res != null)
  {
      Stream resStream = new BufferedStream(res.GetResponseStream());
      TimeStampResponse tsRes = new TimeStampResponse(resStream);
      return tsRes.TimeStampToken.GetEncoded();
  }

  return null;

} }

{% endhighlight %}

{% highlight vb.net tabtitle="VB.NET [Windows-specific]" %}

' External signer class that implements IPdfExternalSigner for signing the document hash. Public Class ExternalSigner Implements IPdfExternalSigner

Private _hashAlgorithm As String

' Gets the hash algorithm used for signing.
Public ReadOnly Property HashAlgorithm() As String Implements IPdfExternalSigner.HashAlgorithm
    Get
        Return _hashAlgorithm
    End Get
End Property

' Constructor that sets the hash algorithm for the signer.
Public Sub New(hashAlgorithm As String)
    _hashAlgorithm = hashAlgorithm
End Sub

' Sign the document hash and return the timestamp response.
Public Function Sign(message As Byte(), ByRef timeStampResponse As Byte()) As Byte() Implements IPdfExternalSigner.Sign
    Dim signedBytes As Byte() = Nothing

    ' Load the digital ID (certificate) from the file system.
    Dim digitalID As New X509Certificate2(Path.GetFullPath("Data/PDF.pfx"), "password123")

    ' Use the appropriate signing algorithm based on the private key type.
    If TypeOf digitalID.PrivateKey Is RSACryptoServiceProvider Then
        ' Use RSACryptoServiceProvider to sign the data.
        Dim rsa As RSACryptoServiceProvider = CType(digitalID.PrivateKey, RSACryptoServiceProvider)
        signedBytes = rsa.SignData(message, HashAlgorithm)
    ElseIf TypeOf digitalID.PrivateKey Is RSACng Then
        ' Use RSACng to sign the data with SHA1 and PKCS1 padding.
        Dim rsa As RSACng = CType(digitalID.PrivateKey, RSACng)
        signedBytes = rsa.SignData(message, HashAlgorithmName.SHA1, RSASignaturePadding.Pkcs1)
    End If

    ' Generate an RFC3161 timestamp token for the signed data.
    timeStampResponse = GetRFC3161TimeStampToken(signedBytes)

    ' Return the signed bytes.
    Return signedBytes
End Function

' Generate the RFC3161 timestamp token using the provided signed data.
Public Function GetRFC3161TimeStampToken(bytes As Byte()) As Byte()
    ' Create a SHA1 hash of the provided signed data.
    Dim sha1 As SHA1 = SHA1CryptoServiceProvider.Create()
    Dim hash As Byte() = sha1.ComputeHash(bytes)

    ' Create a timestamp request using the SHA1 hash.
    Dim reqGen As New TimeStampRequestGenerator()
    reqGen.SetCertReq(True)
    Dim tsReq As TimeStampRequest = reqGen.Generate(TspAlgorithms.Sha1, hash, BigInteger.ValueOf(100))
    Dim tsData As Byte() = tsReq.GetEncoded()

    ' Send the timestamp request to the server.
    Dim req As HttpWebRequest = CType(WebRequest.Create("https://rfc3161.ai.moda"), HttpWebRequest) ' Update your timestamp URI here
    req.Method = "POST"
    req.ContentType = "application/timestamp-query"
    req.Headers.Add("Authorization", "Basic " & Convert.ToBase64String(Encoding.ASCII.GetBytes("9024:yourPass")))
    req.ContentLength = tsData.Length

    ' Write the request data to the request stream.
    Using reqStream As Stream = req.GetRequestStream()
        reqStream.Write(tsData, 0, tsData.Length)
    End Using

    ' Get the response from the timestamp server.
    Dim res As HttpWebResponse = CType(req.GetResponse(), HttpWebResponse)

    ' If a response is received, read and return the timestamp token.
    If res IsNot Nothing Then
        Using resStream As Stream = New BufferedStream(res.GetResponseStream())
            Dim tsRes As New TimeStampResponse(resStream)
            Return tsRes.TimeStampToken.GetEncoded()
        End Using
    End If

    ' Return null if no valid response is received.
    Return Nothing
End Function

End Class

{% endhighlight %}

{% endtabs %}

You can download a complete working sample from GitHub.

Create Long Term Validation (LTV) when signing PDF documents externally

You can create a Long Term validation (LTV) when signing PDF documents externally using your private/public certificates.The following code example shows how to create an LTV when signing a PDF document from external signature using CreateLongTermValidity method in PdfSignature class.

{% tabs %}

{% highlight c# tabtitle="C# [Cross-platform]" playgroundButtonLink="https://raw.githubusercontent.com/SyncfusionExamples/PDF-Examples/master/Digital%20Signature/Create-LTV-when-signing-PDF-documents-externally/.NET/Create-LTV-when-signing-PDF-documents-externally/Program.cs" %}

using Syncfusion.Pdf;
using Syncfusion.Pdf.Parsing;
using Syncfusion.Pdf.Security;
using System.Security.Cryptography;
using System.Security.Cryptography.Pkcs;
using System.Security.Cryptography.X509Certificates;

//Load the PDF document
PdfLoadedDocument document = new PdfLoadedDocument("Input.pdf");

//Get the page of the existing PDF document.
PdfLoadedPage loadedPage = document.Pages[0] as PdfLoadedPage;

//Create a new PDF signature without PdfCertificate instance.
PdfSignature signature = new PdfSignature(document, loadedPage, null, "Signature1");

//Hook up the ComputeHash event.
signature.ComputeHash += Signature_ComputeHash;

//Save the document.
document.Save("SignedDocument.pdf");
//Close the document
document.Close(true);

//Load an existing PDF stream.
PdfLoadedDocument loadedDocument = new PdfLoadedDocument("SignedDocument.pdf");

//Gets the first signature field of the PDF document
PdfLoadedSignatureField signatureField = loadedDocument.Form.Fields[0] as PdfLoadedSignatureField;
PdfSignature pdfSignature = signatureField.Signature;

//Create X509Certificate2 from your certificate to create a long-term validity.
X509Certificate2 x509 = new X509Certificate2(Path.GetFullPath(@"Data/PDF.pfx"), "syncfusion");

//Create LTV with your public certificates.
pdfSignature.CreateLongTermValidity(new List<X509Certificate2> { x509 });

//Save the document
loadedDocument.Save("Output.pdf");
//Close the document.
loadedDocument.Close(true);

void Signature_ComputeHash(object sender, PdfSignatureEventArgs ars)
{
    //Get the document bytes
    byte[] documentBytes = ars.Data;

    SignedCms signedCms = new SignedCms(new ContentInfo(documentBytes), detached: true);

    //Compute the signature using the specified digital ID file and the password
    X509Certificate2 certificate = new X509Certificate2(Path.GetFullPath(@"Data/PDF.pfx"), "syncfusion");
    CmsSigner cmsSigner = new CmsSigner(certificate);

    //Set the digest algorithm SHA256
    cmsSigner.DigestAlgorithm = new Oid("2.16.840.1.101.3.4.2.1");

    signedCms.ComputeSignature(cmsSigner);

    //Embed the encoded digital signature to the PDF document
    ars.SignedData = signedCms.Encode();
}

{% endhighlight %}

{% highlight c# tabtitle="C# [Windows-specific]" %}

using Syncfusion.Pdf;
using Syncfusion.Pdf.Parsing;
using Syncfusion.Pdf.Security;
using System.Security.Cryptography;
using System.Security.Cryptography.Pkcs;
using System.Security.Cryptography.X509Certificates;

//Load an existing PDF document.
PdfLoadedDocument document = new PdfLoadedDocument("Input.pdf");

//Get the page of the existing PDF document.
PdfLoadedPage loadedPage = document.Pages[0] as PdfLoadedPage;

//Create a new PDF signature without PdfCertificate instance.
PdfSignature signature = new PdfSignature(document, loadedPage, null, "Signature1");

//Hook up the ComputeHash event.
signature.ComputeHash += Signature_ComputeHash;

//Save the document.
document.Save("SignedDocument.pdf");
//Close the document
document.Close(true);

//Load an existing PDF stream..
PdfLoadedDocument loadedDocument = new PdfLoadedDocument("SignedDocument.pdf");

//Gets the first signature field of the PDF document
PdfLoadedSignatureField signatureField = loadedDocument.Form.Fields[0] as PdfLoadedSignatureField;
PdfSignature pdfSignature = signatureField.Signature;

//Create X509Certificate2 from your certificate to create a long-term validity.
X509Certificate2 x509 = new X509Certificate2(Path.GetFullPath(@"Data/PDF.pfx"), "syncfusion");

//Create LTV with your public certificates.
pdfSignature.CreateLongTermValidity(new List<X509Certificate2> { x509 });

//Save and close the PDF document
loadedDocument.Save("Output.pdf");
loadedDocument.Close(true);

void Signature_ComputeHash(object sender, PdfSignatureEventArgs ars)
{
    //Get the document bytes
    byte[] documentBytes = ars.Data;

    SignedCms signedCms = new SignedCms(new ContentInfo(documentBytes), detached: true);

    //Compute the signature using the specified digital ID file and the password
    X509Certificate2 certificate = new X509Certificate2(Path.GetFullPath(@"Data/PDF.pfx"), "syncfusion");
    CmsSigner cmsSigner = new CmsSigner(certificate);

    //Set the digest algorithm SHA256
    cmsSigner.DigestAlgorithm = new Oid("2.16.840.1.101.3.4.2.1");

    signedCms.ComputeSignature(cmsSigner);

    //Embed the encoded digital signature to the PDF document
    ars.SignedData = signedCms.Encode();
}

{% endhighlight %}

{% highlight vb.net tabtitle="VB.NET [Windows-specific]" %}

Imports Syncfusion.Pdf
Imports Syncfusion.Pdf.Parsing
Imports Syncfusion.Pdf.Security
Imports System.Security.Cryptography
Imports System.Security.Cryptography.Pkcs
Imports System.Security.Cryptography.X509Certificates

' Load an existing PDF document.
Dim document As New PdfLoadedDocument("Input.pdf")

' Get the page of the existing PDF document.
Dim loadedPage As PdfLoadedPage = TryCast(document.Pages(0), PdfLoadedPage)

' Create a new PDF signature without PdfCertificate instance.
Dim signature As New PdfSignature(document, loadedPage, Nothing, "Signature1")

' Hook up the ComputeHash event.
AddHandler signature.ComputeHash, AddressOf Signature_ComputeHash

' Save the document.
document.Save("SignedDocument")
' Close the document
document.Close(True)

' Load an existing PDF stream.
Dim loadedDocument As New PdfLoadedDocument("SignedDocument")

' Gets the first signature field of the PDF document
Dim signatureField As PdfLoadedSignatureField = TryCast(loadedDocument.Form.Fields(0), PdfLoadedSignatureField)
Dim pdfSignature As PdfSignature = signatureField.Signature

' Create X509Certificate2 from your certificate to create a long-term validity.
Dim x509 As New X509Certificate2(Path.GetFullPath("Data/PDF.pfx"), "syncfusion")

' Create LTV with your public certificates.
pdfSignature.CreateLongTermValidity(New List(Of X509Certificate2) From {x509})

' Save and close the PDF document
loadedDocument.Save("Output.pdf")
loadedDocument.Close(True)

Private Sub Signature_ComputeHash(sender As Object, ars As PdfSignatureEventArgs)
    ' Get the document bytes
    Dim documentBytes As Byte() = ars.Data

    Dim signedCms As New SignedCms(New ContentInfo(documentBytes), True)

    ' Compute the signature using the specified digital ID file and the password
    Dim certificate As New X509Certificate2(Path.GetFullPath("Data/PDF.pfx"), "syncfusion")
    Dim cmsSigner As New CmsSigner(certificate)

    ' Set the digest algorithm SHA256
    cmsSigner.DigestAlgorithm = New Oid("2.16.840.1.101.3.4.2.1")

    signedCms.ComputeSignature(cmsSigner)

    ' Embed the encoded digital signature to the PDF document
    ars.SignedData = signedCms.Encode()
End Sub

{% endhighlight %}

{% endtabs %}

You can download a complete working sample from GitHub.

Digitally sign a PDF document using long-term archive timestamps (LTA)

The PDF LTA signature is the next level of the LTV signature. It follows the standard PAdES B-LTA. According to the standard, the validation-related information of the timestamp is added to the DSS along with other signature information mentioned in the LTV signature.

The document timestamp is also applied to the PDF document, so it provides more viability to the signature. This level is recommended for qualified electronic signatures.

The following code example shows how to sign a PDF document with LTA using TimeStampServer property and EnableLtv property in PdfSignature class.

{% tabs %}

{% highlight c# tabtitle="C# [Cross-platform]" playgroundButtonLink="https://raw.githubusercontent.com/SyncfusionExamples/PDF-Examples/master/Digital%20Signature/Sign_PDF_with_LTA/.NET/Sign_PDF_with_LTA/Program.cs" %}

using Syncfusion.Pdf.Parsing; using Syncfusion.Pdf.Security; using Syncfusion.Pdf;

//Load existing PDF document. FileStream documentStream1 = new FileStream("PDF_Succinctly.pdf", FileMode.Open, FileAccess.Read); PdfLoadedDocument loadedDocument = new PdfLoadedDocument(documentStream1); //Load digital ID with password. FileStream documentStream2 = new FileStream("DigitalSignatureTest.pfx", FileMode.Open, FileAccess.Read); PdfCertificate certificate = new PdfCertificate(documentStream2, "DigitalPass123");

//Create a signature with loaded digital ID. PdfSignature signature = new PdfSignature(loadedDocument, loadedDocument.Pages[0], certificate, "DigitalSignature"); signature.Settings.CryptographicStandard = CryptographicStandard.CADES; signature.Settings.DigestAlgorithm = DigestAlgorithm.SHA256; signature.TimeStampServer = new TimeStampServer(new Uri("http://timestamping.ensuredca.com")); //Enable LTV document. signature.EnableLtv = true;

//Save the PDF document. loadedDocument.Save("LTV_document.pdf"); //Close the document. loadedDocument.Close(true);

//Load existing PDF document. PdfLoadedDocument ltDocument = new PdfLoadedDocument("LTV_document.pdf"); //Load the existing PDF page. PdfLoadedPage lpage = ltDocument.Pages[0] as PdfLoadedPage;

//Create PDF signature with empty certificate. PdfSignature timeStamp = new PdfSignature(lpage, "timestamp"); timeStamp.TimeStampServer = new TimeStampServer(new Uri("http://timestamping.ensuredca.com"));

//Save the document ltDocument.Save("Output.pdf"); //Close the document. ltDocument.Close(true);

{% endhighlight %}

{% highlight c# tabtitle="C# [Windows-specific]" %}

using Syncfusion.Pdf.Parsing; using Syncfusion.Pdf.Security; using Syncfusion.Pdf;

//Load existing PDF document. PdfLoadedDocument loadedDocument = new PdfLoadedDocument("PDF_Succinctly.pdf"); //Load digital ID with password. PdfCertificate certificate = new PdfCertificate("DigitalSignatureTest.pfx", "DigitalPass123");

//Save the PDF document. loadedDocument.Save("LTV_document.pdf"); //Close the document. loadedDocument.Close(true);

//Load existing PDF document. PdfLoadedDocument ltDocument = new PdfLoadedDocument("LTV_document.pdf"); //Load the existing PDF page. PdfLoadedPage lpage = ltDocument.Pages[0] as PdfLoadedPage;

//Save and close the PDF document. ltDocument.Save("PAdES B-LTA.pdf"); ltDocument.Close(true); {% endhighlight %}

{% highlight vb.net tabtitle="VB.NET [Windows-specific]" %}

Imports Syncfusion.Pdf.Parsing Imports Syncfusion.Pdf.Security Imports Syncfusion.Pdf

'Loads a PDF document. Dim loadedDocument As PdfLoadedDocument = New PdfLoadedDocument("PDF_Succinctly.pdf") 'Load digital ID with password. Dim certificate As PdfCertificate = New PdfCertificate("DigitalSignatureTest.pfx", "DigitalPass123")

'Create a signature with loaded digital ID. Dim signature As PdfSignature = New PdfSignature(loadedDocument, loadedDocument.Pages(0), certificate, "DigitalSignature") signature.Settings.CryptographicStandard = CryptographicStandard.CADES signature.Settings.DigestAlgorithm = DigestAlgorithm.SHA256 signature.TimeStampServer = New TimeStampServer(New Uri("http://timestamping.ensuredca.com")) 'Enable LTV document. signature.EnableLtv = True

'Save the document. loadedDocument.Save("LTV_document.pdf") 'Close the document. loadedDocument.Close(True)

'Loads a PDF document. Dim ltDocument As PdfLoadedDocument = New PdfLoadedDocument("LTV_document.pdf") 'Load the existing PDF page. Dim lpage As PdfLoadedPage = TryCast(ltDocument.Pages(0), PdfLoadedPage)

'Create PDF signature with empty certificate. Dim timeStamp As PdfSignature = New PdfSignature(lpage, "timestamp") timeStamp.TimeStampServer = New TimeStampServer(New Uri("http://timestamping.ensuredca.com"))

'Save the document. ltDocument.Save("PAdES B-LTA.pdf") 'Close the document. ltDocument.Close(True)

{% endhighlight %}

{% endtabs %}

You can download a complete working sample from GitHub.

N> When using a custom timestamp server for digital signatures with LTA, you may encounter OverflowException if the estimated signature size is too small.

N> To avoid this, increase the EstimatedSignatureSize property to allocate enough space for the timestamp and LTV data returned by the server.

Digitally sign a PDF document using the Windows certificate store

A Windows certificate store is a secure way to store the digital ID. If a root certificate is added to the Windows certificate store, you do not need to manually add and trust each of the certificates that are already present in the Windows certificate store.

You can retrieve the digital ID X509Certificate2 from the Windows certificate store X509Store and use it to add a digital signature to a PDF document using PdfSignature class.

The following code example shows how to create a PDF digital signature using the Windows certificate store.

{% tabs %}

{% highlight c# tabtitle="C# [Cross-platform]" playgroundButtonLink="https://raw.githubusercontent.com/SyncfusionExamples/PDF-Examples/master/Digital%20Signature/Sign_PDF_Windows_Certificate/.NET/Sign_PDF_Windows_Certificate/Program.cs" %}

using Syncfusion.Pdf.Parsing; using Syncfusion.Pdf.Security; using Syncfusion.Pdf; using System.Security.Cryptography.X509Certificates;

//Initialize the Windows store. X509Store store = new X509Store("MY", StoreLocation.CurrentUser); store.Open(OpenFlags.ReadOnly | OpenFlags.OpenExistingOnly); X509Certificate2Collection collection = (X509Certificate2Collection)store.Certificates; //Find the certificate using thumb print. X509Certificate2Collection fcollection = (X509Certificate2Collection)collection.Find(X509FindType.FindByThumbprint, "F85E1C5D93115CA3F969DA3ABC8E0E9547FCCF5A", true); X509Certificate2 digitalID = collection[0];

//Load existing PDF document. PdfLoadedDocument loadedDocument = new PdfLoadedDocument("PDF_Succinctly.pdf"); //Load X509Certificate2. PdfCertificate certificate = new PdfCertificate(digitalID);

//Create a Revision 2 signature with loaded digital ID. PdfSignature signature = new PdfSignature(loadedDocument, loadedDocument.Pages[0], certificate, "DigitalSignature"); //Changing the digital signature standard and hashing algorithm. signature.Settings.CryptographicStandard = CryptographicStandard.CADES; signature.Settings.DigestAlgorithm = DigestAlgorithm.SHA512;

//Save the document loadedDocument.Save("Output.pdf"); //Close the document. loadedDocument.Close(true);

{% endhighlight %}

{% highlight c# tabtitle="C# [Windows-specific]" %}

using Syncfusion.Pdf.Parsing; using Syncfusion.Pdf.Security; using Syncfusion.Pdf; using System.Security.Cryptography.X509Certificates;

//Load existing PDF document. PdfLoadedDocument loadedDocument = new PdfLoadedDocument("PDF_Succinctly.pdf"); //Load X509Certificate2. PdfCertificate certificate = new PdfCertificate(digitalID);

//Save the PDF document. loadedDocument.Save("WindowsStore.pdf"); //Close the document. loadedDocument.Close(true);

{% endhighlight %}

{% highlight vb.net tabtitle="VB.NET" %}

Imports Syncfusion.Pdf.Parsing Imports Syncfusion.Pdf.Security Imports Syncfusion.Pdf Imports System.Security.Cryptography.X509Certificates

'Initialize the Windows store. Dim store As X509Store = New X509Store("MY", StoreLocation.CurrentUser) store.Open(OpenFlags.[ReadOnly] Or OpenFlags.OpenExistingOnly) 'Find the certificate using thumb print. Dim collection As X509Certificate2Collection = CType(store.Certificates, X509Certificate2Collection) Dim fcollection As X509Certificate2Collection = CType(collection.Find(X509FindType.FindByThumbprint, "F85E1C5D93115CA3F969DA3ABC8E0E9547FCCF5A", True), X509Certificate2Collection) Dim digitalID As X509Certificate2 = fcollection(0)

'Load existing PDF document. Dim loadedDocument As PdfLoadedDocument = New PdfLoadedDocument("PDF_Succinctly.pdf") 'Load X509Certificate2. Dim certificate As PdfCertificate = New PdfCertificate(digitalID) 'Create a Revision 2 signature with loaded digital ID. Dim signature As PdfSignature = New PdfSignature(loadedDocument, loadedDocument.Pages(0), certificate, "DigitalSignature") 'Changing the digital signature standard and hashing algorithm. signature.Settings.CryptographicStandard = CryptographicStandard.CADES signature.Settings.DigestAlgorithm = DigestAlgorithm.SHA512

'Save the PDF document. loadedDocument.Save("WindowsStore.pdf") 'Close the document. loadedDocument.Close(True)

{% endhighlight %}

{% endtabs %}

You can download a complete working sample from GitHub.

Adding a signature validation appearance based on the signature

You can add the dynamic signature validation appearance to the signature field by enabling the EnableValidationAppearance property available in the PdfSignature class, the appearance will change based on the PDF reader validation.

Refer to the following code sample.

{% tabs %}

{% highlight c# tabtitle="C# [Cross-platform]" playgroundButtonLink="https://raw.githubusercontent.com/SyncfusionExamples/PDF-Examples/master/Digital%20Signature/Adding-a-signature-validation-appearance-in-a-PDF/.NET/Adding-a-signature-validation-appearance-in-a-PDF/Program.cs" %}

using Syncfusion.Drawing; using Syncfusion.Pdf; using Syncfusion.Pdf.Graphics; using Syncfusion.Pdf.Security;

//Creates a new PDF document PdfDocument document = new PdfDocument(); //Adds a new page PdfPageBase page = document.Pages.Add(); //Create PDF graphics for the page. PdfGraphics graphics = page.Graphics;

//Creates a certificate instance from the PFX file with private key FileStream certificateStream = new FileStream("PDF.pfx", FileMode.Open, FileAccess.Read); PdfCertificate pdfCert = new PdfCertificate(certificateStream, "password123"); //Creates a digital signature PdfSignature signature = new PdfSignature(document, page, pdfCert, "Signature"); //Sets an image for the signature field FileStream imageStream = new FileStream("signature.jpg", FileMode.Open, FileAccess.Read); //Sets an image for signature field PdfBitmap signatureImage = new PdfBitmap(imageStream); //Sets enable signature validation appearance signature.EnableValidationAppearance = true; //Sets signature information signature.Bounds = new RectangleF(new PointF(0, 0), signatureImage.PhysicalDimension); signature.SignedName = "Syncfusion"; signature.ContactInfo = "johndoe@owned.us"; signature.LocationInfo = "Honolulu, Hawaii"; signature.Reason = "I am author of this document."; //Draws the signature image signature.Appearance.Normal.Graphics.DrawImage(signatureImage, 0, 0);

//Save the document document.Save("Output.pdf"); //Close the document. document.Close(true);

{% endhighlight %}

{% highlight c# tabtitle="C# [Windows-specific]" %}

using System.Drawing; using Syncfusion.Pdf; using Syncfusion.Pdf.Graphics; using Syncfusion.Pdf.Security;

//Creates a new PDF document PdfDocument document = new PdfDocument();
//Add a new page PdfPageBase page = document.Pages.Add(); //Create PDF graphics for the page PdfGraphics graphics=page.Graphics;

//Creates a certificate instance from the PFX file with private key
PdfCertificate pdfCert = new PdfCertificate(@"PDF.pfx", "password123"); //Creates a digital signature PdfSignature signature = new PdfSignature(document, page, pdfCert, "Signature"); //Sets an image for the signature field PdfBitmap signatureImage = new PdfBitmap(@"signature.jpg"); //Sets enable signature validation appearance signature.EnableValidationAppearance = true; //Sets signature information signature.SignedName = "Syncfusion"; signature.ContactInfo = "johndoe@owned.us"; signature.LocationInfo = "Honolulu, Hawaii"; signature.Reason = "I am author of this document."; //Draw the signature image
signature.Appearance.Normal.Graphics.DrawImage(signatureImage, 0, 0);

//Save and close document document.Save("Output.pdf"); document.Close( true );

{% endhighlight %}

{% highlight vb.net tabtitle="VB.NET [Windows-specific]" %}

Imports System.Drawing Imports Syncfusion.Pdf Imports Syncfusion.Pdf.Graphics Imports Syncfusion.Pdf.Security

'Creates a certificate instance from the PFX file with private key Dim pdfCert As New PdfCertificate("PDF.pfx", "password123") 'Creates a digital signature Dim signature As New PdfSignature(document, page, pdfCert, "Signature") 'Sets an image for the signature field Dim signatureImage As New PdfBitmap("signature.jpg") 'Sets enable signature validation appearance
signature.EnableValidationAppearance = True 'Sets signature info signature.Bounds = New RectangleF(New PointF(0, 0), signatureImage.PhysicalDimension) signature.SignedName = "Syncfusion" signature.ContactInfo = "johndoe@owned.us" signature.LocationInfo = "Honolulu, Hawaii" signature.Reason = "I am author of this document." 'Draws the signature image signature.Appearance.Normal.Graphics.DrawImage(signatureImage, 0, 0)

'Save and close the document document.Save("Output.pdf") document.Close(True)

{% endhighlight %}

{% endtabs %}

You can download a complete working sample from GitHub.

Adding a timestamp in digital signature

Essential^® PDF allows you to add timestamp in the digital signature of the PDF document using TimeStampServer property in PdfSignature class. The following code example explains the same.

{% tabs %}

{% highlight c# tabtitle="C# [Cross-platform]" playgroundButtonLink="https://raw.githubusercontent.com/SyncfusionExamples/PDF-Examples/master/Digital%20Signature/Adding-a-timestamp-in-digital-signature-of-PDF/.NET/Adding-a-timestamp-in-digital-signature-of-PDF/Program.cs" %}

using Syncfusion.Drawing; using Syncfusion.Pdf; using Syncfusion.Pdf.Graphics; using Syncfusion.Pdf.Security;

//Creates a certificate instance from PFX file with private key FileStream certificateStream = new FileStream("PDF.pfx", FileMode.Open, FileAccess.Read); PdfCertificate pdfCert = new PdfCertificate(certificateStream, "password123"); //Creates a digital signature PdfSignature signature = new PdfSignature(document, page, pdfCert, "Signature"); //Sets an image for signature field FileStream imageStream = new FileStream("syncfusion_logo.jpeg", FileMode.Open, FileAccess.Read); //Sets an image for signature field PdfBitmap image = new PdfBitmap(imageStream); //Adds time stamp by using the server URI and credentials signature.TimeStampServer = new TimeStampServer(new Uri("http://syncfusion.digistamp.com"), "user", "123456"); //Sets signature info signature.Bounds = new RectangleF(new PointF(0, 0), image.PhysicalDimension); signature.SignedName = "Syncfusion"; signature.ContactInfo = "johndoe@owned.us"; signature.LocationInfo = "Honolulu, Hawaii"; signature.Reason = "I am author of this document."; //Draws the signature image signature.Appearance.Normal.Graphics.DrawImage(image, 0, 0);

//Save the document document.Save("Output.pdf"); //Close the document. document.Close(true);

{% endhighlight %}

{% highlight c# tabtitle="C# [Windows-specific]" %}

using System.Drawing; using Syncfusion.Pdf; using Syncfusion.Pdf.Graphics; using Syncfusion.Pdf.Security;

//Creates a new PDF document PdfDocument document = new PdfDocument(); //Adds a new page PdfPage page = document.Pages.Add(); //Create PDF graphics for the page PdfGraphics graphics = page.Graphics;

//Creates a certificate instance from PFX file with private key PdfCertificate pdfCert = new PdfCertificate(@"PDF.pfx", "password123"); //Creates a digital signature PdfSignature signature = new PdfSignature(page, pdfCert, "Signature"); //Change the digital signature standard and hashing algorithm signature.Settings.CryptographicStandard = CryptographicStandard.CADES; signature.Settings.DigestAlgorithm = DigestAlgorithm.SHA512; //Sets an image for signature field PdfBitmap image = new PdfBitmap(@"syncfusion_logo.jpeg"); //Adds time stamp by using the server URI and credentials signature.TimeStampServer = new TimeStampServer(new Uri("http://syncfusion.digistamp.com"), "user", "123456"); //Sets signature info signature.Bounds = new RectangleF(new PointF(0, 0), image.PhysicalDimension); signature.SignedName = "Syncfusion"; signature.ContactInfo = "johndoe@owned.us"; signature.LocationInfo = "Honolulu, Hawaii"; signature.Reason = "I am author of this document."; //Draws the signature image signature.Appearance.Normal.Graphics.DrawImage(image, 0, 0);

//Save and close the document document.Save("Output.pdf"); document.Close(true);

{% endhighlight %}

{% highlight vb.net tabtitle="VB.NET [Windows-specific]" %}

Imports System.Drawing Imports Syncfusion.Pdf Imports Syncfusion.Pdf.Graphics Imports Syncfusion.Pdf.Security

'Creates a new PDF document Dim document As New PdfDocument() 'Adds a new page Dim page As PdfPage = document.Pages.Add() 'Create PDF graphics for the page Dim graphics As PdfGraphics = page.Graphics

'Creates a certificate instance from PFX file with private key Dim pdfCert As New PdfCertificate("PDF.pfx", "password123") 'Creates a digital signature Dim signature As New PdfSignature(page, pdfCert, "Signature") 'Sets an image for signature field Dim image As New PdfBitmap("syncfusion_logo.jpeg") 'Adds time stamp by using the server URI and credentials signature.TimeStampServer = New TimeStampServer(New Uri("http://syncfusion.digistamp.com"), "user", "123456") 'Sets signature info signature.Bounds = New RectangleF(New PointF(0, 0), image.PhysicalDimension) signature.SignedName = "Syncfusion" signature.ContactInfo = "johndoe@owned.us" signature.LocationInfo = "Honolulu, Hawaii" signature.Reason = "I am author of this document." 'Draws the signature image signature.Appearance.Normal.Graphics.DrawImage(image, 0, 0)

'Save and close the document document.Save("Output.pdf") document.Close(True)

{% endhighlight %}

{% endtabs %}

You can download a complete working sample from GitHub.

Adding a timestamp to PDF document

You can add timestamp to the PDF document using TimeStampServer property in PdfSignature class. The following code example explains the same.

{% tabs %}

{% highlight c# tabtitle="C# [Cross-platform]" playgroundButtonLink="https://raw.githubusercontent.com/SyncfusionExamples/PDF-Examples/master/Digital%20Signature/Adding-a-timestamp-to-PDF-document/.NET/Adding-a-timestamp-to-PDF-document/Program.cs" %}

using Syncfusion.Pdf; using Syncfusion.Pdf.Security;

//Create a new pdf document PdfDocument document = new PdfDocument(); //Adds a new page PdfPage page = document.Pages.Add();

//Creates a digital signature PdfSignature signature = new PdfSignature(page, "Signature"); //Add the time stamp by using the server URI signature.TimeStampServer = new TimeStampServer(new Uri("http://syncfusion.digistamp.com"), "user", "123456");

//Save the document document.Save("Output.pdf"); //Close the document. document.Close(true);

{% endhighlight %}

{% highlight c# tabtitle="C# [Windows-specific]" %}

using Syncfusion.Pdf; using Syncfusion.Pdf.Security;

//Create a new PDF document PdfDocument document = new PdfDocument(); //Add a new page PdfPage page = document.Pages.Add();

//Save and close the document document.Save("Output.pdf"); document.Close(true);

{% endhighlight %}

{% highlight vb.net tabtitle="VB.NET [Windows-specific]" %}

Imports Syncfusion.Pdf Imports Syncfusion.Pdf.Security

'Creates a new PDF document Dim document As New PdfDocument() 'Adds a new page Dim page As PdfPage = document.Pages.Add()

'Creates a digital signature Dim signature As New PdfSignature(page, "Signature") 'Adds time stamp by using the server URI signature.TimeStampServer = New TimeStampServer(New Uri("http://syncfusion.digistamp.com"), "user", "123456")

'Save and close the document document.Save("Output.pdf") document.Close(True)

{% endhighlight %}

{% endtabs %}

You can download a complete working sample from GitHub.

Adding a timestamp to existing PDF document

You can add timestamp to the existing PDF document using TimeStampServer property in PdfSignature class. The following code example explains the same.

{% tabs %}

{% highlight c# tabtitle="C# [Cross-platform]" playgroundButtonLink="https://raw.githubusercontent.com/SyncfusionExamples/PDF-Examples/master/Digital%20Signature/Adding-a-timestamp-to-an-existing-PDF/.NET/Adding-a-timestamp-to-an-existing-PDF/Program.cs" %}

using Syncfusion.Pdf; using Syncfusion.Pdf.Parsing; using Syncfusion.Pdf.Security;

//Load the PDF document PdfLoadedDocument loadedDocument = new PdfLoadedDocument("Input.pdf"); //Gets the page PdfLoadedPage page = loadedDocument.Pages[0] as PdfLoadedPage;

//Save the document loadedDocument.Save("Output.pdf"); //Close the document. loadedDocument.Close(true);

{% endhighlight %}

{% highlight c# tabtitle="C# [Windows-specific]" %}

using Syncfusion.Pdf; using Syncfusion.Pdf.Parsing; using Syncfusion.Pdf.Security;

//Load the existing PDF document PdfLoadedDocument loadedDocument = new PdfLoadedDocument("Input.pdf"); //Add a new page PdfLoadedPage page = loadedDocument.Pages[0] as PdfLoadedPage;

//Save the PDF document loadedDocument.Save("Output.pdf"); //Close the document loadedDocument.Close(true);

{% endhighlight %}

{% highlight vb.net tabtitle="VB.NET [Windows-specific]" %}

Imports Syncfusion.Pdf.Parsing Imports Syncfusion.Pdf Imports Syncfusion.Pdf.Security

'Load the PDF document Dim document As New PdfLoadedDocument("Input.pdf") 'Gets the first page of the document Dim page As PdfLoadedPage = TryCast(document.Pages(0), PdfLoadedPage)

'Save and close the document document.Save("Output.pdf") document.Close(True)

{% endhighlight %}

{% endtabs %}

You can download a complete working sample from GitHub.

Retrieve certificate details from an existing signed PDF document

The Essential^® PDF provides support to get the certificate details from an existing signed PDF document such as,

Signed date
Expiry date
Signed name
Subject name
Issuer name
Certificate distinguished names (country, state, street, email, organization, organization unit, locality, and more).

You can get the above certificate details from an existing signed PDF document using ValidFrom and ValidTo property.The following code example explains the same.

{% tabs %}

{% highlight c# tabtitle="C# [Cross-platform]" playgroundButtonLink="https://raw.githubusercontent.com/SyncfusionExamples/PDF-Examples/master/Digital%20Signature/Retrieve-certificate-details-from-an-existing-PDF/.NET/Retrieve-certificate-details-from-an-existing-PDF/Program.cs" %}

using Syncfusion.Pdf.Parsing; using Syncfusion.Pdf.Security;

//Load the PDF document PdfLoadedDocument loadedDocument = new PdfLoadedDocument("Input.pdf"); //Get the signature field PdfLoadedSignatureField signatureField = loadedDocument.Form.Fields[0] as PdfLoadedSignatureField;

//Close the document loadedDocument.Close(true);

{% endhighlight %}

{% highlight c# tabtitle="C# [Windows-specific]" %}

using Syncfusion.Pdf.Parsing; using Syncfusion.Pdf.Security;

//Load the existing signed PDF PdfLoadedDocument loadedDocument = new PdfLoadedDocument("SignedDocument.pdf"); //Load the PDF form PdfLoadedForm loadedForm = loadedDocument.Form as PdfLoadedForm; //Get the signature field PdfLoadedSignatureField signatureField = loadedForm.Fields[0] as PdfLoadedSignatureField;

//Get the certificate PdfCertificate certificate = signatureField.Signature.Certificate; //Get the signed date DateTime date = signatureField.Signature.SignedDate; //Get the signed name string name = signatureField.Signature.SignedName; //Get the certificate names based on their distinguished name. string subjectName = certificate.SubjectName string subjectCountry = certificate.GetValue(PdfCertificateDistinguishedName.Country, PdfCertificateField.Subject); string subjectOrganization = certificate.GetValue(PdfCertificateDistinguishedName.Organization, PdfCertificateField.Subject); //Issuer details string issuerName = certificate.IssuerName; string issuerOrganization = certificate.GetValue(PdfCertificateDistinguishedName.Organization, PdfCertificateField.Issuer); string issuerCountry = certificate.GetValue(PdfCertificateDistinguishedName.Country, PdfCertificateField.Issuer); //Get certificate validation date information DateTime validFrom = certificate.ValidFrom; DateTime validTo = certificate.ValidTo;

//Close the document loadedDocument.Close(true);

{% endhighlight %}

{% highlight vb.net tabtitle="VB.NET [Windows-specific]" %}

Imports Syncfusion.Pdf.Parsing Imports Syncfusion.Pdf.Security

'Load the existing signed PDF Dim loadedDocument As PdfLoadedDocument = New PdfLoadedDocument("../../Signed.pdf") 'Load the PDF form Dim loadedForm As PdfLoadedForm = TryCast(loadedDocument.Form, PdfLoadedForm) 'Get the signature field Dim signatureField As PdfLoadedSignatureField = TryCast(loadedForm.Fields(0), PdfLoadedSignatureField)

'Get the certificate Dim certificate As PdfCertificate = signatureField.Signature.Certificate 'Get the signed date Dim signedDate As DateTime = signatureField.Signature.SignedDate 'Get the signed name Dim name As String = signatureField.Signature.SignedName 'Get the certificate names based on their distinguished name Dim subjectName As String = certificate.SubjectName Dim subjectCountry As String = certificate.GetValue(PdfCertificateDistinguishedName.Country, PdfCertificateField.Subject) Dim subjectOrganization As String = certificate.GetValue(PdfCertificateDistinguishedName.Organization, PdfCertificateField.Subject) 'Issuer details Dim issuerName As String = certificate.IssuerName Dim issuerOrganization As String = certificate.GetValue(PdfCertificateDistinguishedName.Organization, PdfCertificateField.Issuer) Dim issuerCountry As String = certificate.GetValue(PdfCertificateDistinguishedName.Country, PdfCertificateField.Issuer) 'Get certificate validation date information Dim validFrom As DateTime = certificate.ValidFrom Dim validTo As DateTime = certificate.ValidTo

'Close the PDF document loadedDocument.Close(True)

{% endhighlight %}

{% endtabs %}

You can download a complete working sample from GitHub.

Enable Long Term Validation (LTV) PDF signature

The Essential^® PDF supports creating long term signature validation when signing the PDF document. The LTV signature allows you to check the validity of a signature long after the document was signed. To achieve long term validation, all the required elements for signature validation must be embedded in the signed PDF.

N> The resulted PDF document size will be large since all the necessary signature information, Certificate Revocation List (CRL), and Online Certificate Status Protocol (OCSP) are embedded.

The following code example explains how to create LTV PDF using EnableLtv property in PdfSignature class when signing the PDF document.

{% tabs %}

{% highlight c# tabtitle="C# [Cross-platform]" playgroundButtonLink="https://raw.githubusercontent.com/SyncfusionExamples/PDF-Examples/master/Digital%20Signature/Enable-LTV-PDF-signature/.NET/Enable-LTV-PDF-signature/Program.cs" %}

using Syncfusion.Drawing;
using Syncfusion.Pdf;
using Syncfusion.Pdf.Graphics;
using Syncfusion.Pdf.Parsing;
using Syncfusion.Pdf.Security;

//Creates a new PDF document.
PdfDocument document = new PdfDocument();

//Adds a new page.
PdfPageBase page = document.Pages.Add();

//Create graphics for the page. 
PdfGraphics graphics = page.Graphics;

//Creates a certificate instance from PFX file with private key.
FileStream certificateStream = new FileStream(Path.GetFullPath(@"Data/PDF.pfx"), FileMode.Open, FileAccess.Read);
PdfCertificate pdfCert = new PdfCertificate(certificateStream, "DigitalPass123");

//Creates a digital signature.
PdfSignature signature = new PdfSignature(document, page, pdfCert, "Signature");
signature.Settings.CryptographicStandard = CryptographicStandard.CADES;
signature.Settings.DigestAlgorithm = DigestAlgorithm.SHA256;

document.Save("SignedDocument.pdf");
//Close the document
document.Close(true);

//Load an existing PDF stream.
PdfLoadedDocument loadedDocument = new PdfLoadedDocument("SignedDocument.pdf");

//Gets the first signature field of the PDF document
PdfLoadedSignatureField signatureField = loadedDocument.Form.Fields[0] as PdfLoadedSignatureField;
PdfSignature pdfSignature = signatureField.Signature;

//Enable LTV on Signature.
pdfSignature.EnableLtv = true;

//Save the document
loadedDocument.Save("Output.pdf");
//Close the document.
loadedDocument.Close(true);

{% endhighlight %}

{% highlight c# tabtitle="C# [Windows-specific]" %}

using System.Drawing;
using Syncfusion.Pdf;
using Syncfusion.Pdf.Graphics;
using Syncfusion.Pdf.Parsing;
using Syncfusion.Pdf.Security;

//Creates a new PDF document.
PdfDocument document = new PdfDocument();

//Adds a new page.
PdfPageBase page = document.Pages.Add();

//Create graphics for the page. 
PdfGraphics graphics = page.Graphics;

//Creates a certificate instance from PFX file with private key.
PdfCertificate pdfCert = new PdfCertificate(Path.GetFullPath(@"Data/PDF.pfx"), "DigitalPass123");

//Creates a digital signature.
PdfSignature signature = new PdfSignature(document, page, pdfCert, "Signature");
signature.Settings.CryptographicStandard = CryptographicStandard.CADES;
signature.Settings.DigestAlgorithm = DigestAlgorithm.SHA256;

//Save the document.

document.Save("SignedDocument.pdf");
//Close the document
document.Close(true);

//Load an existing PDF stream.
PdfLoadedDocument loadedDocument = new PdfLoadedDocument("SignedDocument.pdf");

//Gets the first signature field of the PDF document
PdfLoadedSignatureField signatureField = loadedDocument.Form.Fields[0] as PdfLoadedSignatureField;
PdfSignature pdfSignature = signatureField.Signature;

//Enable LTV on Signature.
pdfSignature.EnableLtv = true;

//Save and close the document
loadedDocument.Save("Output.pdf");
loadedDocument.Close(true);

{% endhighlight %}

{% highlight vb.net tabtitle="VB.NET [Windows-specific]" %}

Imports System.Drawing
Imports Syncfusion.Pdf
Imports Syncfusion.Pdf.Graphics
Imports Syncfusion.Pdf.Parsing
Imports Syncfusion.Pdf.Security

' Creates a new PDF document.
Dim document As New PdfDocument()

' Adds a new page.
Dim page As PdfPageBase = document.Pages.Add()

' Create graphics for the page.
Dim graphics As PdfGraphics = page.Graphics

' Creates a certificate instance from PFX file with private key.
Dim pdfCert As New PdfCertificate(Path.GetFullPath("Data/PDF.pfx"), "DigitalPass123")

' Creates a digital signature.
Dim signature As New PdfSignature(document, page, pdfCert, "Signature")
signature.Settings.CryptographicStandard = CryptographicStandard.CADES
signature.Settings.DigestAlgorithm = DigestAlgorithm.SHA256

' Save the document.
document.Save("SignedDocument.pdf")

' Close the document.
document.Close(True)

' Load an existing PDF stream.
Dim loadedDocument As New PdfLoadedDocument("SignedDocument.pdf")

' Gets the first signature field of the PDF document.
Dim signatureField As PdfLoadedSignatureField = TryCast(loadedDocument.Form.Fields(0), PdfLoadedSignatureField)
Dim pdfSignature As PdfSignature = signatureField.Signature

' Enable LTV on Signature.
pdfSignature.EnableLtv = True

' Save and close the document.
loadedDocument.Save("Output.pdf")
loadedDocument.Close(True)

{% endhighlight %}

{% endtabs %}

You can download a complete working sample from GitHub.

Adding a digital signature with customization

The PdfSignatureSettings allows you to add customized digital signatures to the PDF document.

Adding a digital signature with CAdES format

As per the PDF specification 2.0, now Syncfusion PDF library supports digital signature based on CAdES (CMS Advanced Electronics Signature). The CAdES based digital signature can remain valid for long periods, even if underlying cryptographic algorithms are broken. Using the API CryptographicStandard, you can change the standard between CMS (Cryptographic Message Syntax) and CAdES.

The following code example explains how to add a digital signature with cryptographic standard as CAdES through CryptographicStandard Enum when creating the PDF document.

{% tabs %}

{% highlight c# tabtitle="C# [Cross-platform]" playgroundButtonLink="https://raw.githubusercontent.com/SyncfusionExamples/PDF-Examples/master/Digital%20Signature/Adding-a-digital-signature-with-CAdES-format/.NET/Adding-a-digital-signature-with-CAdES-format/Program.cs" %}

using Syncfusion.Drawing; using Syncfusion.Pdf; using Syncfusion.Pdf.Graphics; using Syncfusion.Pdf.Security;

//Create a new PDF document PdfDocument document = new PdfDocument(); //Add a new page PdfPageBase page = document.Pages.Add(); //Create PDF graphics for the page PdfGraphics graphics = page.Graphics;

//Sets an image for signature field FileStream imageStream = new FileStream("signature.jpg", FileMode.Open, FileAccess.Read); //Sets an image for signature field PdfBitmap signatureImage = new PdfBitmap(imageStream); //Sets signature information signature.Bounds = new RectangleF(new PointF(0, 0), signatureImage.PhysicalDimension); signature.SignedName = "Syncfusion"; signature.ContactInfo = "johndoe@owned.us"; signature.LocationInfo = "Honolulu, Hawaii"; signature.Reason = "I am author of this document."; //Draws the signature image signature.Appearance.Normal.Graphics.DrawImage(signatureImage, 0, 0);

//Save the document document.Save("Output.pdf"); //Close the document. document.Close(true);

{% endhighlight %}

{% highlight c# tabtitle="C# [Windows-specific]" %}

using System.Drawing; using Syncfusion.Pdf; using Syncfusion.Pdf.Graphics; using Syncfusion.Pdf.Security;

//Creates a certificate instance from PFX file with private key PdfCertificate pdfCert = new PdfCertificate(@"PDF.pfx", "password123"); //Creates a digital signature PdfSignature signature = new PdfSignature(document, page, pdfCert, "Signature"); //Sets signature settings to customize cryptographic standard specified PdfSignatureSettings settings = signature.Settings; settings.CryptographicStandard = CryptographicStandard.CADES;

//Sets an image for signature field PdfBitmap signatureImage = new PdfBitmap(@"signature.jpg"); //Sets signature information signature.Bounds = new RectangleF(new PointF(0, 0), signatureImage.PhysicalDimension); signature.SignedName = "Syncfusion"; signature.ContactInfo = "johndoe@owned.us"; signature.LocationInfo = "Honolulu, Hawaii"; signature.Reason = "I am author of this document."; //Draws the signature image signature.Appearance.Normal.Graphics.DrawImage(signatureImage, 0, 0);

//Save and close the document document.Save("Output.pdf"); document.Close(true);

{% endhighlight %}

{% highlight vb.net tabtitle="VB.NET [Windows-specific]" %}

Imports System.Drawing Imports Syncfusion.Pdf Imports Syncfusion.Pdf.Graphics Imports Syncfusion.Pdf.Security

'Creates a certificate instance from PFX file with private key Dim pdfCert As New PdfCertificate("PDF.pfx", "password123") 'Creates a digital signature Dim signature As New PdfSignature(document, page, pdfCert, "Signature") 'Sets signature settings to customize cryptographic standard specified Dim settings As PdfSignatureSettings = signature.Settings settings.CryptographicStandard = CryptographicStandard.CADES

'Sets an image for signature field Dim signatureImage As New PdfBitmap("signature.jpg") 'Sets signature info signature.Bounds = New RectangleF(New PointF(0, 0), signatureImage.PhysicalDimension) signature.SignedName = "Syncfusion" signature.ContactInfo = "johndoe@owned.us" signature.LocationInfo = "Honolulu, Hawaii" signature.Reason = "I am author of this document." 'Draws the signature image signature.Appearance.Normal.Graphics.DrawImage(signatureImage, 0, 0)

'Save and close the document document.Save("Output.pdf") document.Close(True)

{% endhighlight %}

{% endtabs %}

You can download a complete working sample from GitHub.

Customize digestion algorithm

In addition, you can now set the different message digest algorithm to sign PDF document using the DigestAlgorithm enum available in the class PdfSignatureSettings.

The following message digest algorithms are now supported:

SHA1
SHA256
SHA384
SHA512
RIPEMD160

The following code example explains how to add a digital signature with various digest algorithms to the PDF document by specifying the DigestAlgorithm property as SHA256 through DigestAlgorithm enum in PdfSignatureSettings class.

{% tabs %}

{% highlight c# tabtitle="C# [Cross-platform]" playgroundButtonLink="https://raw.githubusercontent.com/SyncfusionExamples/PDF-Examples/master/Digital%20Signature/Add-digital-signature-with-digest-algorithm/.NET/Add-digital-signature-with-digest-algorithm/Program.cs" %}

using Syncfusion.Drawing; using Syncfusion.Pdf; using Syncfusion.Pdf.Graphics; using Syncfusion.Pdf.Security;

//Save the document document.Save("Output.pdf"); //Close the document. document.Close(true);

{% endhighlight %}

{% highlight c# tabtitle="C# [Windows-specific]" %}

using System.Drawing; using Syncfusion.Pdf; using Syncfusion.Pdf.Graphics; using Syncfusion.Pdf.Security;

//Save and close the document document.Save("Output.pdf"); document.Close(true);

{% endhighlight %}

{% highlight vb.net tabtitle="VB.NET [Windows-specific]" %}

Imports System.Drawing Imports Syncfusion.Pdf Imports Syncfusion.Pdf.Graphics Imports Syncfusion.Pdf.Security

'Creates a certificate instance from PFX file with private key Dim pdfCert As New PdfCertificate("PDF.pfx", "password123") 'Creates a digital signature Dim signature As New PdfSignature(document, page, pdfCert, "Signature") 'Sets signature settings to customize digest algorithm specified Dim settings As PdfSignatureSettings = signature.Settings settings.DigestAlgorithm = DigestAlgorithm.SHA256

'Save and close the document document.Save("Output.pdf") document.Close(True)

{% endhighlight %}

{% endtabs %}

You can download a complete working sample from GitHub.

Digital signature validation

Added the support to validate the digital signatures in an existing PDF document. Digital signature validation covers the following steps to ensure the validity of the signatures:

Validate the document modification.
Validate the certificate chain.
Ensure the signature with timestamp time.
Check the revocation status of the certificate with OCSP and CRL.
Ensure the multiple digital signatures.

You can use the ValidateSignature method available in the PdfLoadedSignatureField class to validate the digital signature.

You can get the overall status from the IsSignatureValid property available in the PdfSignatureValidationResult class.

The following code example explains how to validate the digitally signed PDF document signature.

{% tabs %}

{% highlight c# tabtitle="C# [Cross-platform]" playgroundButtonLink="https://raw.githubusercontent.com/SyncfusionExamples/PDF-Examples/master/Digital%20Signature/Validate-the-digitally-signed-PDF-signature/.NET/Validate-the-digitally-signed-PDF-signature/Program.cs" %}

using Syncfusion.Pdf.Parsing; using Syncfusion.Pdf.Security; using System.Security.Cryptography.X509Certificates;

// Load the signed PDF document PdfLoadedDocument loadedDocument = new PdfLoadedDocument("Input.pdf");

// Retrieve the first signature field from the PDF form PdfLoadedSignatureField signatureField = loadedDocument.Form.Fields[0] as PdfLoadedSignatureField;

// Create a certificate collection to hold trusted root certificates for validation X509CertificateCollection collection = new X509CertificateCollection();

// Load the root certificate from a PFX file (includes private key) FileStream certificateStream = new FileStream(Path.GetFullPath(@"Data/PDF.pfx"), FileMode.Open, FileAccess.Read); byte[] data = new byte[certificateStream.Length]; certificateStream.Read(data, 0, data.Length);

// Create an X509Certificate2 instance using the loaded certificate data and password X509Certificate2 certificate = new X509Certificate2(data, "syncfusion");

// Add the certificate to the validation collection collection.Add(certificate);

// Validate the signature using the provided certificate collection PdfSignatureValidationResult result = signatureField.ValidateSignature(collection);

// Initialize flag to detect timestamp signatures bool isTimeStampSignature = false;

// Check if the TimeStampInformation object is not null if (result.TimeStampInformation != null) { // Check if the signature is a document timestamp if (result.TimeStampInformation.IsDocumentTimeStamp) { isTimeStampSignature = true; Console.WriteLine("Signature is a document timestamp signature."); }

// Retrieve signer certificates if available
PdfSignerCertificate[] certificates = result.TimeStampInformation.SignerCertificates;
if (certificates != null && certificates.Length > 0)
{
    Console.WriteLine($"Retrieved {certificates.Length} signer certificate(s).");
}
else
{
    Console.WriteLine("No signer certificates found.");
}

// Retrieve the main certificate
X509Certificate2 certificate2 = result.TimeStampInformation.Certificate;
if (certificate2 != null)
{
    Console.WriteLine($"Certificate Subject: {certificate2.Subject}");
}
else
{
    Console.WriteLine("No certificate found.");
}

// Retrieve timestamp date
DateTime dateTime = result.TimeStampInformation.Time;
Console.WriteLine($"Timestamp Date: {dateTime}");

// Retrieve timestamp policy ID
string policyID = result.TimeStampInformation.TimeStampPolicyId;
if (!string.IsNullOrEmpty(policyID))
{
    Console.WriteLine($"Timestamp Policy ID: {policyID}");
}
else
{
    Console.WriteLine("No Timestamp Policy ID found.");
}

// Check if the timestamp is valid
bool valid = result.TimeStampInformation.IsValid;
Console.WriteLine($"Timestamp Validity: {(valid ? "Valid" : "Invalid")}");

} else { Console.WriteLine("TimeStampInformation is null. Cannot retrieve timestamp details."); }

// Check if the signature is valid SignatureStatus status = result.SignatureStatus;

// Check if the document has been modified after signing bool isModified = result.IsDocumentModified;

// Check if Long-Term Validation (LTV) is enabled in the signature bool isLtvEnabled = result.LtvVerificationInfo.IsLtvEnabled;

// Check if Certificate Revocation List (CRL) data is embedded in the PDF bool isCrlEmbedded = result.LtvVerificationInfo.IsCrlEmbedded;

// Check if Online Certificate Status Protocol (OCSP) data is embedded in the PDF bool isOcspEmbedded = result.LtvVerificationInfo.IsOcspEmbedded;

// Output the validation results to the console Console.WriteLine("Document modified: " + isModified); Console.WriteLine("LTV enabled: " + isLtvEnabled); Console.WriteLine("CRL embedded: " + isCrlEmbedded); Console.WriteLine("OCSP embedded: " + isOcspEmbedded);

// Extract and display signature certificate details string issuerName = signatureField.Signature.Certificate.IssuerName; DateTime validFrom = signatureField.Signature.Certificate.ValidFrom; DateTime validTo = signatureField.Signature.Certificate.ValidTo; string signatureAlgorithm = result.SignatureAlgorithm; DigestAlgorithm digestAlgorithm = result.DigestAlgorithm;

Console.WriteLine("Issuer Name: " + issuerName); Console.WriteLine("Valid From: " + validFrom); Console.WriteLine("Valid To: " + validTo); Console.WriteLine("Signature Algorithm: " + signatureAlgorithm); Console.WriteLine("Digest Algorithm: " + digestAlgorithm);

// Extract and display revocation validation details RevocationResult revocationDetails = result.RevocationResult; RevocationStatus revocationStatus = revocationDetails.OcspRevocationStatus; bool isRevokedCRL = revocationDetails.IsRevokedCRL;

Console.WriteLine("Revocation Status: " + revocationStatus); Console.WriteLine("Is Revoked CRL: " + isRevokedCRL);

// Close the loaded PDF document and release resources loadedDocument.Close(true);