TX Text Control provides a powerful API to sign PDF documents with signature fields and digital signatures. This article shows how to sign a PDF document with a digital signature using the TX Text Control API and to set custom signer information.

Pre-Populated Signer Information

Signer information, such as the reason for signing and the signer's address, can be added at the design time of the document or template. This information is stored in the internal TX Text Control document format and can be used to pre-fill the signature fields.

The following screenshots show a signature field and the ribbon bar with the pre-populated information:

When signing the document with a digital signature, the pre-populated information is used automatically.

Custom Signer Information

When signing a document with a digital signature, the signer information can be set programmatically using the SignerData property. This property is an instance of the SignerData class that provides the following properties:

The following code snippet shows how to set the signer information for a signature field:

using System.Security.Cryptography.X509Certificates;
using TXTextControl;

using (TXTextControl.ServerTextControl tx = new TXTextControl.ServerTextControl())
{
        tx.Create();
        
        tx.Load("signature.tx", TXTextControl.StreamType.InternalUnicodeFormat);

        // create a certificate
        X509Certificate2 cert = new X509Certificate2("textcontrolself.pfx", "123");

        // create a list of digital signatures
        var digitalSignatures = new List<DigitalSignature>();

        foreach (SignatureField signatureField in tx.SignatureFields)
        {
                signatureField.SignerData = new SignerData(
                        "John Doe", 
                        "CEO", 
                        "11 Main Street, New York, NY 10001, USA",
                        "john@doe.com",
                        "Contract signature");

                // time stamp server
                var timeStampServer = "http://timestamp.digicert.com";

                // create a digital signature object
                DigitalSignature digitalSignature = new DigitalSignature(cert, timeStampServer, signatureField.Name);
                
                // add the digital signature to the list
                digitalSignatures.Add(digitalSignature);
        }

        // create save settings
        SaveSettings saveSettings = new SaveSettings()
        {
                CreatorApplication = "Your Application",
                SignatureFields = digitalSignatures.ToArray()
        };

        // save the document as PDF
        tx.Save("results_signed.pdf", StreamType.AdobePDFA, saveSettings);
}

Additionally, the time server is added to the digital signature. The timeServerURL parameter is set to the URL of the time server.

When the document is signed, the signature field is updated with the custom signer information:

When the document is opened in Adobe Acrobat Reader, the custom signer information is displayed in the signature properties.

Conclusion

TX Text Control provides a powerful API to sign PDF documents with signature fields and digital signatures. The signer information can be pre-populated at the design time of the document or set programmatically using the SignerData property.