test.cs

[HttpPost]
public string ExportPDF()
{
  Stream inputStream = Request.InputStream;
  inputStream.Position = 0;

  StreamReader str = new StreamReader(inputStream);
  string sBuf = str.ReadToEndAsync().Result;

  TXTextControl.Web.MVC.DocumentViewer.Models.SignatureData data =
    JsonConvert.DeserializeObject<TXTextControl.Web.MVC.DocumentViewer.Models.SignatureData>(sBuf);

  byte[] bPDF;

  // create temporary ServerTextControl
  using (TXTextControl.ServerTextControl tx = new TXTextControl.ServerTextControl())
  {
    tx.Create();

    // load the document
    tx.Load(Convert.FromBase64String(data.SignedDocument.Document), TXTextControl.BinaryStreamType.InternalUnicodeFormat);

    FlattenFormFields(tx);

    X509Certificate2 cert = new X509Certificate2(Server.MapPath("~/App_Data/textcontrolself.pfx"), "123");

    TXTextControl.SaveSettings saveSettings = new TXTextControl.SaveSettings()
    {
      CreatorApplication = "TX Text Control Sample Application",
      //DigitalSignature = new TXTextControl.DigitalSignature(cert, null),
           SignatureFields = new DigitalSignature[] { 
              new TXTextControl.DigitalSignature(cert, null, "txsign"),
              new TXTextControl.DigitalSignature(cert, null, "txsign_init")}
    };

    // save the document as PDF
    tx.Save(out bPDF, TXTextControl.BinaryStreamType.AdobePDFA, saveSettings);
  }

  // return as Base64 encoded string
  return Convert.ToBase64String(bPDF);
}