Also see the various PDF modules on CPAN.

The best approach always depends on what exactly you need to do. I for one have good experiences with emitting LaTeX files from perl, and then running pdflatex to create PDF files from that. But of course it depends on your use case if that's a suitable approach for you.

For example if you already have a PDF template and merely need to replace some text or images, other approaches might work better.

PDF::API2 is a pretty mature Perl module for PDF creation — though it needs a bit of "getting used to" its docs.   However, as has already been said, what is best depends on your specific requirements...

On one of my previous jobs we used Cairo to generate PDFs, after falling into problems with PDF::API2 (I wouldn't recommend this one). It is very fast and has very moderate memory requirements, but it is a generic graphic library and lack support for many useful PDF features like indexes and links, so may not suit your needs. Also I had some positive experience with CAM::PDF.

PDF::Create is a simple pdf creator.If you need bit more complicated works to be done you can choose PDF::API2