PDF Clown
http://www.stefanochizzolini.it/en/projects/clown/index.html
Documentation
http://www.stefanochizzolini.it/en/projects/clown/doc/index.html
Example: Indexing PDF- once again with a big red nose
http://weblogs.asp.net/bleroy/indexing-pdf-once-again-with-a-big-red-nose