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How to apply one or more digital signatures to a PDF using C# and VB.NET?
5 mins read
Syncfusion Essential PDF is a .NET Core PDF library used to create, read, and edit PDF documents. Using this library, you can apply one or more digital signature to a PDF document using C# and VB.NET.
Steps to apply one or more digital signature to PDF document programmatically:
- Create a new C# ASP.NET Core Web application project.
- Select Web application pattern (Model-View-Controller) for the project.
- Install the Syncfusion.Pdf.Net.Core NuGet package as reference to your .NET Standard application from NuGet.org.
- A default controller with name HomeController.cs gets added on creation of ASP.NET Core project. Include the following namespaces in that HomeController.cs file.
C#
using Syncfusion.Pdf; using Syncfusion.Pdf.Parsing; using Syncfusion.Pdf.Security; using Syncfusion.Pdf.Graphics;
VB.NET
Imports Syncfusion.Pdf Imports Syncfusion.Pdf.Parsing Imports Syncfusion.Pdf.Security Imports Syncfusion.Pdf.Graphics
- A default action method named Index will be present in HomeController.cs. Right-click the Index method and select Go To View where you will be directed to its associated view pageIndex.cshtml.
- Add a new button in the Index.cshtml as follows.
<h2>Click the button to generate PDF</h2> @using (Html.BeginForm("GeneratePDF", "Home", FormMethod.Post)) { <input type="submit" value="GeneratePDF" /> }
- Add a new action method GeneratePDF in HomeController.cs and include the following code snippet to create a PDF file and download it.
C#
//Load the PDF document
FileStream docStream = new FileStream("SignatureFields.pdf", FileMode.Open, FileAccess.Read);
PdfLoadedDocument loadedDocument = new PdfLoadedDocument(docStream);
//Gets the first page of the document
PdfLoadedPage page = loadedDocument.Pages[0] as PdfLoadedPage;
//Gets the first signature field of the PDF document
PdfLoadedSignatureField signatureField1 = loadedDocument.Form.Fields[0] as PdfLoadedSignatureField;
//Creates a certificate
FileStream certificateStream1 = new FileStream("PDF.pfx", FileMode.Open, FileAccess.Read);
PdfCertificate certificate1 = new PdfCertificate(certificateStream1, "syncfusion");
signatureField1.Signature = new PdfSignature(loadedDocument, page, certificate1, "Signature", signatureField1);
FileStream imageStream = new FileStream("Student Signature.jpg", FileMode.Open, FileAccess.Read);
//Draw image
PdfBitmap signatureImage = new PdfBitmap(imageStream);
signatureField1.Signature.Appearance.Normal.Graphics.DrawImage(signatureImage, 0, 0, 90, 20);
//Save the document into stream
MemoryStream stream = new MemoryStream();
loadedDocument.Save(stream);
//Load the signed PDF document
PdfLoadedDocument signedDocument = new PdfLoadedDocument(stream);
//Load the PDF page
PdfLoadedPage loadedPage = signedDocument.Pages[0] as PdfLoadedPage;
//Gets the first signature field of the PDF document
PdfLoadedSignatureField signatureField2 = signedDocument.Form.Fields[1] as PdfLoadedSignatureField;
signatureField2.Signature = new PdfSignature(signedDocument, loadedPage, certificate1, "Signature", signatureField2);
FileStream imageStream1 = new FileStream("Teacher Signature.png", FileMode.Open, FileAccess.Read);
PdfBitmap signatureImage1 = new PdfBitmap(imageStream1);
//Draw image
signatureField2.Signature.Appearance.Normal.Graphics.DrawImage(signatureImage1, 0, 0, 90, 20);
//Saving the PDF to the MemoryStream
MemoryStream signedStream = new MemoryStream();
signedDocument.Save(signedStream);
//Set the position as '0'.
signedStream.Position = 0;
//Download the PDF document in the browser
FileStreamResult fileStreamResult = new FileStreamResult(signedStream, "application/pdf");
fileStreamResult.FileDownloadName = "DigitalSignatureSample.pdf";
return fileStreamResult;
VB.NET
'Load the PDF document
Dim docStream As FileStream = New FileStream("SignatureFields.pdf", FileMode.Open, FileAccess.Read)
Dim loadedDocument As PdfLoadedDocument = New PdfLoadedDocument(docStream)
'Gets the first page of the document
Dim page As PdfLoadedPage = TryCast(loadedDocument.Pages(0), PdfLoadedPage)
'Gets the first page of the document
Dim signatureField1 As PdfLoadedSignatureField = TryCast(loadedDocument.Form.Fields(0), PdfLoadedSignatureField)
'Creates a certificate
Dim certificateStream1 As FileStream = New FileStream("PDF.pfx", FileMode.Open, FileAccess.Read)
Dim certificate1 As PdfCertificate = New PdfCertificate(certificateStream1, "syncfusion")
signatureField1.Signature = New PdfSignature(loadedDocument, page, certificate1, "Signature", signatureField1)
Dim imageStream As FileStream = New FileStream("Student Signature.jpg", FileMode.Open, FileAccess.Read)
'Draw image
Dim signatureImage As PdfBitmap = New PdfBitmap(imageStream)
signatureField1.Signature.Appearance.Normal.Graphics.DrawImage(signatureImage, 0, 0, 90, 20)
'Save the document into stream
Dim stream As MemoryStream = New MemoryStream()
loadedDocument.Save(stream)
'Load the signed PDF document
Dim signedDocument As PdfLoadedDocument = New PdfLoadedDocument(stream)
'Load the PDF page
Dim loadedPage As PdfLoadedPage = TryCast(signedDocument.Pages(0), PdfLoadedPage)
Dim signatureField2 As PdfLoadedSignatureField = TryCast(signedDocument.Form.Fields(1), PdfLoadedSignatureField)
signatureField2.Signature = New PdfSignature(signedDocument, loadedPage, certificate1, "Signature", signatureField2)
Dim imageStream1 As FileStream = New FileStream("Teacher Signature.png", FileMode.Open, FileAccess.Read)
'Draw image
Dim signatureImage1 As PdfBitmap = New PdfBitmap(imageStream1)
signatureField2.Signature.Appearance.Normal.Graphics.DrawImage(signatureImage1, 0, 0, 90, 20)
'Saving the PDF to the MemoryStream
Dim signedStream As MemoryStream = New MemoryStream()
signedDocument.Save(signedStream)
'Set the position as '0'.
signedStream.Position = 0
'Download the PDF document in the browser
Dim fileStreamResult As FileStreamResult = New FileStreamResult(signedStream, "application/pdf")
fileStreamResult.FileDownloadName = "DigitalSignatureSample.pdf"
Return fileStreamResult
A complete working sample can be downloaded from DigitalSignatureSample.zip.
By executing the program, you will get the PDF document as follows. 
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 redacting PDF document and protect PDF document with code examples.
An online sample link to digitally sign a PDF document.
Refer here to learn more about digitally sign PDF files of Syncfusion Essential PDF.
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.
