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How to digitally sign PDF using X509 Certificate2 in C# and VB.NET?

7 mins read

PDF documents are digitally signed using x509 certificates such as .pfx files with private keys and support for Hardware Security Module (HSM), Online Certificate Status Protocol (OCSP), Certificate Revocation List (CRL), and Windows Certificate Store to offer authenticity and integrity.

Syncfusion Essential® PDF is a .NET PDF Library used to create, read, and edit PDF documents. Using this library, you can add digital signature to the PDF document using X509Certificate2 class object in C# and VB.NET.

Steps to digitally sign a PDF document using X509Certificate2 class object programmatically:

  1. Create a new C# console application project. Creation of console application
  2. Install the Syncfusion.Pdf.WinForms NuGet package as reference to your .NET Framework application from NuGet.org. Nuget package reference
  3. Include the following namespace in the Program.cs file.

C#

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

 

VB.NET

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

 

  1. Use the following code snippet to add a digital signature in the PDF document.

C#

// Creates a new PDF document
PdfDocument document = new PdfDocument();
//Adds a new page
PdfPageBase page = document.Pages.Add();
PdfGraphics graphics = page.Graphics;
//Creating a X509Certificate2 instance from PFX file with private key
X509Certificate2 cert = new X509Certificate2("pdf.pfx", "syncfusion");
//Creating PdfCertificate object with  X509Certificate2 class object
PdfCertificate pdfCert = new PdfCertificate(cert);
//Creates a digital signature
PdfSignature signature = new PdfSignature(document, page, pdfCert, "Signature");
//Sets an image for signature field
PdfBitmap signatureImage = new PdfBitmap(@"signature.png");
//Sets signature information
signature.Bounds = new RectangleF(0, 0, 200, 100);
signature.ContactInfo = "johndoe@owned.us";
signature.LocationInfo = "Honolulu, Hawaii";
signature.Reason = "I am author of this document.";
//Draws the signature image
graphics.DrawImage(signatureImage, signature.Bounds);
//Save the document
document.Save("Signature.pdf");
//Close the document
document.Close(true);
//This will open the PDF file so, the result will be seen in default PDF Viewer
Process.Start("Signature.pdf");

 

VB.NET

'Creates a new PDF document
Dim document As New PdfDocument()
'Adds a new page
Dim page As PdfPageBase = document.Pages.Add()
Dim graphics As PdfGraphics = page.Graphics
'Creating a X509Certificate2 instance from PFX file with private key
Dim cert As New X509Certificate2("pdf.pfx", "syncfusion")
'Creating PdfCertificate object with  X509Certificate2 class object
Dim pdfCert As New PdfCertificate(cert)
'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.png")
'Sets signature information
signature.Bounds = New RectangleF(0, 0, 200, 100)
signature.ContactInfo = "johndoe@owned.us"
signature.LocationInfo = "Honolulu, Hawaii"
signature.Reason = "I am author of this document."
'Draws the signature image
graphics.DrawImage(signatureImage, signature.Bounds)
'Save the document
document.Save("Signature.pdf")
'Close the document
document.Close(True)
'This will open the PDF file so, the result will be seen in default PDF Viewer
 Process.Start("Signature.pdf")

 

Download the working sample from DigitalSignature.zip

By executing the program, you will get the PDF document as follows. Output PDF document

Take a moment to peruse the documentation, where you can find other options like adding a digital signature using stream, signing an existing document, adding a timestamp in digital signature and features like protect PDF documents with code examples.

Refer here to explore the rich set of Syncfusion Essential® PDF features.

An online sample link to generate Digitally signed PDF document

Note:

Starting with v16.2.0.x, if you reference Syncfusion® assemblies from trial setup or from the NuGet feed, include a license key in your projects. Refer to link to learn about generating and registering Syncfusion® license key in your application to use the components without trail message.


Conclusion
I hope you enjoyed learning on How to digitally sign PDF using X509Certificate2 in C# and VB.NET.
You can refer to our WinForms PDF feature tour page to know about its other groundbreaking feature representations and documentation, and how to quickly get started for configuration specifications. You can also explore our WinForms PDF example to understand how to create and manipulate data.
For current customers, you can check out our components from the License and Downloads page. If you are new to Syncfusion®, you can try our 30-day free trial to check out our other controls.
If you have any queries or require clarifications, please let us know in the comments section below. You can also contact us through our support forumsDirect-Trac, or feedback portal. We are always happy to assist you!
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