test.cs

public static void SignFields() {
  using (ServerTextControl tx = new ServerTextControl()) {

    tx.Create();

    // create a signature field
    SignatureField signatureField = new SignatureField(
      new System.Drawing.Size(2000, 2000), "txsign", 10);

    // set image representation
    signatureField.Image = new SignatureImage("signature.svg", 0);

    // insert the field
    tx.SignatureFields.Add(signatureField, -1);

    // create a digital signature (for each field, if required)
    DigitalSignature digitalSignature = new DigitalSignature(
      new System.Security.Cryptography.X509Certificates.X509Certificate2(
        "textcontrolself.pfx", "123"), null, "txsign");

    // apply the signatures to the SaveSettings
    SaveSettings saveSettings = new SaveSettings() {
      SignatureFields = new DigitalSignature[] { digitalSignature }
    };

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