test.cs

public static void SignDocument() {

  using (ServerTextControl tx = new ServerTextControl()) {

    tx.Create();

    // add dummy text
    tx.Text = "This is a signed document";

    SaveSettings saveSettings = new SaveSettings();

    // add digital signature to sign complete document
    saveSettings.DigitalSignature = new DigitalSignature(
      new System.Security.Cryptography.X509Certificates.X509Certificate2(
        "textcontrolself.pfx", "123"), null);

    // export to PDF
    tx.Save("signed_documents.pdf", StreamType.AdobePDF, saveSettings);
  }

}