Verify Digital signatures in the document Leave feedback

GroupDocs.Signature provides DigitalVerifyOptions class to specify different options for digital signatures verification.

Note

Verification performs two independent checks. First the signature itself is verified cryptographically: if the document was altered after signing, the result is not valid regardless of any other option. Then any criteria you set on DigitalVerifyOptions - certificate, subject name, issuer name, signing time, reason, contact or location - are matched. Both must pass for IsValid to be true. For PDF documents the cryptographic check was added in GroupDocs.Signature for .NET 26.9; earlier versions compared only the criteria.

Here are the steps to verify Digital signature within the document with GroupDocs.Signature:

• Create new instance of Signature class and pass source document path as a constructor parameter.
• Instantiate the DigitalVerifyOptions object according to your requirements and specify verification options
• Call Verify method of Signature class instance and pass DigitalVerifyOptions to it.

This example shows how to verify Digital signature in the document.

using (Signature signature = new Signature("sample.pdf"))
{
    DigitalVerifyOptions options = new DigitalVerifyOptions("certificate.pfx")
    {
        Password = "1234567890",
        // the subject of the signing certificate must contain this text
        SubjectName = "John Smith",
        // the signing reason stored in the PDF signature must be equal to this text
        Reason = "Approved"
    };
    // verify document signatures
    VerificationResult result = signature.Verify(options);
    if (result.IsValid)
    {
        Console.WriteLine("\nDocument was verified successfully!");
    }
    else
    {
        Console.WriteLine("\nDocument failed verification process.");
    }
}

Not every property of DigitalVerifyOptions applies to every document format. A property that does not apply is ignored, so it can neither reject nor accept a signature. For example, Comments has no effect on a PDF document, because PDF signatures have no comment field: use Reason instead.

SubjectName and IssuerName match when the subject or issuer of the signing certificate contains the value, case-sensitive. They apply to PDF documents starting with GroupDocs.Signature for .NET 26.9; earlier versions ignored them there.

To learn more about document eSign features, please refer to the advanced usage section.

You may easily run the code above and see the feature in action in our GitHub examples:

• GroupDocs.Signature for .NET examples, plugins, and showcase
• GroupDocs.Signature for Java examples, plugins, and showcase
• Document Signature for .NET MVC UI Example
• Document Signature for .NET App WebForms UI Example
• Document Signature for Java App Dropwizard UI Example
• Document Signature for Java Spring UI Example

Along with the full-featured .NET library, we provide simple but powerful free online apps.

To sign PDF, Word, Excel, PowerPoint, and other documents you can use the online apps from the GroupDocs.Signature App Product Family.