test.cs

[HttpPost]
public string MergeAnnotations() {

   Stream inputStream = Request.InputStream;
   inputStream.Position = 0;

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

   List<List<TXTextControl.SignatureAnnotation.Annotation>> annotations =
      JsonConvert.DeserializeObject<List<List<TXTextControl.SignatureAnnotation.Annotation>>>(sBuf);

   byte[] bTx;
   int iPageNumber = 0;

   string prePng = "data:image/png;base64,";
   string preSvg = "data:image/svg+xml;utf8,";

   // calculate the current resolution
   var dpi = 1440 / DocumentController.DpiX;

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

      // load the document
      tx.Load(Server.MapPath("~/App_Data/Documents/template_sign.tx"), StreamType.InternalUnicodeFormat);

      // loop through the array of annotations
      foreach (List<TXTextControl.SignatureAnnotation.Annotation> pages in annotations) {

         iPageNumber++;

         foreach (TXTextControl.SignatureAnnotation.Annotation annotation in pages) {

            // handle only signatures
            if (annotation.pen.type != "signature")
               continue;

            byte[] bytes;

            // get SVG or PNG as bytes and remove the prefix
            if (annotation.image.StartsWith(prePng))
               bytes = Convert.FromBase64String(annotation.image.Remove(0, prePng.Length));
            else
               bytes = Encoding.UTF8.GetBytes(annotation.image.Remove(0, preSvg.Length));

            // create a memory stream from SVG
            using (MemoryStream ms = new MemoryStream(
               bytes, 0, bytes.Length, writable: false, publiclyVisible: true)) {

               // TX image from memory stream
               TXTextControl.Image img = new TXTextControl.Image(ms);

               // add the image as a fixed object on the current page (array)
               tx.Images.Add(
                  img,
                  iPageNumber,
                  new System.Drawing.Point(0, (int)(annotation.location.y * dpi)),
                  TXTextControl.ImageInsertionMode.BelowTheText | TXTextControl.ImageInsertionMode.FixedOnPage);

               // set the location
               img.Location = new System.Drawing.Point(
                     (int)(annotation.location.x * dpi),
                     img.Location.Y);

            }

         }

      }

      // save the document as PDF
      tx.Save(out bTx, TXTextControl.BinaryStreamType.InternalUnicodeFormat);
   }

   // return as base64 encoded string
   return Convert.ToBase64String(bTx);
}