An alternative could be using an external program like http://www.pdflabs.com/tools/pdftk-the-pdf-toolkit/ and so something like:
$ pdftk file.pdf dump_data_fields
and then process the output. However, this would involve a lot of parsing logic and output processing. Plus, if you cannot install binaries on your server, never mind. :)
It might be just simpler to do as hoppa mentioned.
Edit: This question might be a duplicate of The best pratice to parse PDF forms fields with PHP5 that question has an interesting comment!
