SignWithQRCode.cs

// For complete examples and data files, please go to https://github.com/groupdocs-signature/GroupDocs.Signature-for-.NET
string filePath = "../../SampleFiles/sample.pdf";
string fileName = Path.GetFileName(filePath);

string outputFilePath = Path.Combine("../../Output/", "SignWithQRCode", fileName);

using (Signature signature = new Signature(filePath))
{
    // create QRCode option with predefined QRCode text
    QrCodeSignOptions options = new QrCodeSignOptions("JohnSmith")
    {
        // setup QRCode encoding type
        EncodeType = QrCodeTypes.QR,

        // set signature position
        Left = 100,
        Top = 100
    };

    // sign document to file
    signature.Sign(outputFilePath, options);
}
Console.WriteLine("\nSource document signed successfully.\nFile saved at " + outputFilePath);