in reply to
pdf custom properties
This book is largely Perl based.
PDF Hacks - 100 Industrial Strength Tips and Tools
Author Sid Steward.
It'll probably be on Oreilly Bookshelf if you can't get it from Amazon.
Pdf is a tricky and complex format but primarily text based so Perl can often hack into it.
Have you tried writing a marker string using Acrobat Pro or similar, then search for the marker with vim. If it remains plain text you can probably find it and identify postscript placeholders in the pdf file that give you the location. You can then use regex to write your text data on the same placeholder location in other pdf files. (I've used this technique before on pdf and it often works a treat but sometimes it's not that easy)
Remember though, a pdf isn't a simple data file, it's a postscript program so you'll break it if you aren't careful.
There are some pdf APIs available - pdflib, etc. But they aren't cheap.