test.cs

using (TXTextControl.ServerTextControl tx = new ServerTextControl()) {
  tx.Create();
  tx.Load("test.docx", TXTextControl.StreamType.WordprocessingML);

  List<TXTextControl.DigitalSignature> digitalSignatures = new List<DigitalSignature>();

  foreach (SignatureField field in tx.SignatureFields) {
     digitalSignatures.Add(new DigitalSignature(
     new System.Security.Cryptography.X509Certificates.X509Certificate2(
        "textcontrolself.pfx", "123"), null, field.Name));
  }

  SaveSettings saveSettings = new SaveSettings() {
     SignatureFields = digitalSignatures.ToArray()
  };

  tx.Save("results.pdf", TXTextControl.StreamType.AdobePDF, saveSettings);
}