How to stamp a new PDF file with an image watermark while converting PPT to PDF?

This video shows how to add an image watermark to stamp the PDF file which is converted from PPT by using A-PDF PPT to PDF. See more at: http://a-pdf.com/faq/how-to-stamp-an-image-watermark-to-new-pdf-file-when-converting-ppt-to-pdf.htm