python - How can I add transparent watermark to PDF printout using reportlab python library

Question

I have to draw a watermark in my dynamically generated PDF Print.

I did it using the pyPdf library(By merging the Original PDF and the PDF with watermark). http://wa5pb.freeshell.org/motd/?p=769

My problem is, I have to make the watermark image transparent, without using the mask parameter of drawImage feature in reportlab library, Since it is manual. Any suggestions?

Thanks!.