How to Apply One or More Digital Signatures to a PDF Using C# or VB.NET

Syncfusion Essential® PDF is a ASP.NET Core PDF library that allows you to create, read, and edit PDF documents. It also enables you to apply one or more digital signatures to a PDF document using C# or VB.NET.

Steps to apply one or more digital signatures to a PDF document programmatically:

1. Create a New Project: Start by setting up a new C# ASP.NET Core Web application. Select the Model-View-Controller (MVC) pattern for your project.

2.Install Necessary Packages: Add the Syncfusion.Pdf.Net.Core NuGet package to your .NET Standard application from NuGet.org.

3. Configure the Application: On project creation, a default controller named HomeController.cs is added. Include the necessary namespaces

C#

VB.NET

4.Implement the PDF Generation: Find the Index method in HomeController.cs. Add a button in Index.cshtml to trigger PDF generation.

<h2>Click the button to generate PDF</h2>
@using (Html.BeginForm("GeneratePDF", "Home", FormMethod.Post))
{
    <input type="submit" value="Generate PDF" />
}

5. Add Digital Signatures: Implement the `GeneratePDF` method in `HomeController.cs` to apply the digital signatures using the following code.

C#

// Load the PDF document
using (FileStream docStream = new FileStream("SignatureFields.pdf", FileMode.Open, FileAccess.Read))
{
    PdfLoadedDocument loadedDocument = new PdfLoadedDocument(docStream);
    // Get the first page of the document
    PdfLoadedPage page = loadedDocument.Pages[0] as PdfLoadedPage;
    // Get the first signature field of the PDF document
    PdfLoadedSignatureField signatureField1 = loadedDocument.Form.Fields[0] as PdfLoadedSignatureField;
    // Create a certificate
    using (FileStream certificateStream1 = new FileStream("PDF.pfx", FileMode.Open, FileAccess.Read))
    {
        PdfCertificate certificate1 = new PdfCertificate(certificateStream1, "syncfusion");

        // Apply the signature to the first signature field
        signatureField1.Signature = new PdfSignature(loadedDocument, page, certificate1, "Signature", signatureField1);
        // Load the student signature image
        using (FileStream imageStream = new FileStream("Student Signature.jpg", FileMode.Open, FileAccess.Read))
        {

            // Draw the student signature image
            PdfBitmap signatureImage = new PdfBitmap(imageStream);
            signatureField1.Signature.Appearance.Normal.Graphics.DrawImage(signatureImage, 0, 0, 90, 20);
        }
        // Save the document into a stream
        using (MemoryStream stream = new MemoryStream())
        {
            loadedDocument.Save(stream);
            stream.Position = 0;

            // Load the signed PDF document
            using (PdfLoadedDocument signedDocument = new PdfLoadedDocument(stream))
            {
                // Get the first page of the signed document
                PdfLoadedPage loadedPage = signedDocument.Pages[0] as PdfLoadedPage;
                // Get the second signature field of the PDF document
                PdfLoadedSignatureField signatureField2 = signedDocument.Form.Fields[1] as PdfLoadedSignatureField;
                // Apply the signature to the second signature field
                signatureField2.Signature = new PdfSignature(signedDocument, loadedPage, certificate1, "Signature", signatureField2);
                // Load the teacher signature image
                using (FileStream imageStream1 = new FileStream("Teacher Signature.png", FileMode.Open, FileAccess.Read))
                {
                    // Draw the teacher signature image
                    PdfBitmap signatureImage1 = new PdfBitmap(imageStream1);                         signatureField2.Signature.Appearance.Normal.Graphics.DrawImage(signatureImage1, 0, 0, 90, 20);
                }
                // Save the final signed PDF to a FileStream
                using (FileStream finalFileStream = new FileStream("Output.pdf", FileMode.Create, FileAccess.Write))
                {
                    signedDocument.Save(finalFileStream);

                }        
            }
        }
    }
}

VB.NET

A complete working sample is available for download:DigitalSignatureSample.zip.

By executing the program, the output PDF document will be generated as shown below:

Conclusion

I hope you enjoyed learning about how to apply one or more digital signatures to a PDF in ASP.NET Core.

You can refer to our ASP.NET Core 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 ASP.NET Core PDF example to understand how to create and manipulate data in the .NET PDF. 

For current customers, you can check out our Document processing libraries from the License and Downloads page. If you are new to Syncfusion®, you can try our 30-day free trial to check out our ASP.NET Core PDF and other .NET Core 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 forums, Direct-Trac, or feedback portal. We are always happy to assist you!