1. I created pdf file with watermark (any text) on your demo (http://www.aspose.com/demos/.net-components/aspose.pdf/csharp/PdfDemos/Stamps/AddTextStamp.aspx).
2. Take this file and sent it to @gmail.com as attachment.
3. Open this attachment in https://mail.google.com/.
Problem: Watermark is displayed incorrectly on the gmail viewer.
I added watermarks via another program - watermarks are displayed correctly.
I attached pdf and screenshot from gmail viewer - please see and investigate my problem.
This issue is very important for our clients.