This is a reply to the posting by "Filth" about empty PDF - "rocksky" has more or less the same solution.

The trick is here:

              stamp.FormFlattening = true;
              // very important to keep the MemoryStream intact

              stamp.Writer.CloseStream = false;


It took me a good deal of head-scratching to find the solution a while back, and I've posted a blog-posting about it on my (infrequently updated)  blog: