tx.cs

// create a non-UI ServerTextControl instance
using (TXTextControl.ServerTextControl tx = new TXTextControl.ServerTextControl()) {

  tx.Create();

  // load the PDF document
  TXTextControl.LoadSettings ls = new TXTextControl.LoadSettings();
  tx.Load("document.pdf", TXTextControl.StreamType.AdobePDF, ls);

  // read the attachments
  TXTextControl.EmbeddedFile[] files = ls.EmbeddedFiles;

  // find the specific attachment and save it
  foreach(TXTextControl.EmbeddedFile file in files) {
    if (file.Description == "My Text File") {
      string sAttachment = Encoding.UTF8.GetString((byte[])file.Data);
      System.IO.File.WriteAllText("attachment_read.txt", sAttachment);

      break;
    }
  }
}