Simply search at this site :) The questions about PDF documents are asked quite often. There are many PDF-related modules at CPAN but there is no module that fits all needs. PDF::API2 seems to be the most powerful - and the most complicated.
It may also depend on what you're actually editing. If you wish to update interactive forms on a PDF, the module PDF::Reuse will come in very handy. It is on CPAN.
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Keep your concentration here and now where it belongs - Qui-Gon Jinn
Edited by planetscape - moved content out of signature (readability)