good library for pdf

[Enrique Palomo Jiménez]

Hi all,

I want to take an existing pdf and add it a non-opaque watermark.
I have tried it in postscript but postscript hava an opaque imaging model.
Pdf allows it. I can do it with acrobat 6.0, but i need to add the watermark in batch mode or inside an application.

I've found lowagie library for java.

Anyone knows if there is something similar for python??

must i begin to learn java?? 

Regards