Steps for Adding Digital Signature to PDF Documents

DigitalSignatureNamespaces.cs

using GroupDocs.Signature;
using GroupDocs.Signature.Domain;
using GroupDocs.Signature.Options;

DigitalVerifyOptions.cs

DigitalVerifyOptions options = new DigitalVerifyOptions("certificate.pfx")
{
    Comments = "Test comment"
};

LoadDigitallySignedPDF.cs

using (Signature signature = new Signature("sample.pdf"))
{
    // Your code goes here.
}

VerificationResult.cs

if (result.IsValid)
{
    Console.WriteLine("\nDocument was verified successfully!");
}
else
{
    Console.WriteLine("\nDocument failed verification process.");
}

VerifyDigitalSignature.cs

// verify document signatures
VerificationResult result = signature.Verify(options);

VerifyDigitalSignatureInPDFDocument.cs

using GroupDocs.Signature;
using GroupDocs.Signature.Domain;
using GroupDocs.Signature.Options;

using (Signature signature = new Signature("sample.pdf"))
{
    DigitalVerifyOptions options = new DigitalVerifyOptions("certificate.pfx")
    {
        Comments = "Test comment"
    };
    // verify document signatures
    VerificationResult result = signature.Verify(options);
    if (result.IsValid)
    {
        Console.WriteLine("\nDocument was verified successfully!");
    }
    else
    {
        Console.WriteLine("\nDocument failed verification process.");
    }
}