test.cs

using System.Text;

using (TXTextControl.ServerTextControl tx = new TXTextControl.ServerTextControl()) {
   tx.Create();
   tx.Text = "This is a sample PDF document with an attachment";

   byte[] baAttachment = Encoding.ASCII.GetBytes("This is a textual attachment.");

   // create a new embedded file
   TXTextControl.EmbeddedFile efAttachment =
       new TXTextControl.EmbeddedFile("attachment.tx", baAttachment, null) {
          Description = "My embedded text file."
       };

   // add the embedded file to TextControl
   tx.DocumentSettings.EmbeddedFiles =
       new TXTextControl.EmbeddedFile[] { efAttachment };

   // save the document
   tx.Save("mypdf.pdf", TXTextControl.StreamType.AdobePDF);
}