I've been hearing about The GNU PDF Library since 2007. Since then I've been looking forward to see this tool in the wild, but four years have passed and it seems to me that this is a painfully long time. I'm aware of the complexities of the project, but as I recall the GNU Foundation have marked it as a top priority project. What is going on?
There seems to be some activity on http://lists.gnu.org/archive/html/pdf-devel/. Also, see http://gnupdf.org/manuals/gnupdf-hg-manual/html_node/Information-for-Newcomers.html#Information-for-Newcomers for information about cloning their repository. Specifically do
$ bzr branch bzr://bzr.savannah.gnu.org/pdf/libgnupdf/trunk libgnupdf
Bazaar is a distributed version control system, and its command line client is called
Looking at the repository is a good way to determine activity. You can see the logs by changing directory into the repository
libgnupdf and doing
bzr log -v | less. My two cents are that 929 revisions in slightly less than 4 years isn't so bad. Such projects usually have a shortage of manpower and of course everyone is a volunteer. If you have any specific questions, I'm sure the developers would be happy to answer, as long as you ask nicely.
The FSF has recently dropped GNU PDF from their list of priority projects because libraries like poppler, podofo, MuPDF and Apache PDFBox have developed quite nicely over the last years. Given the speed of development of GNU PDF over the last years I'm tempted to call it glacial: They seem to spend all their time at building foundations and up to now don't seem to have at least a minimal parser. It seems GNU Hurd will be finished before GNU PDF.
See here for a list of PDF libraries.
In addition to Faheem answer - it is good to look on Ohloh stats (here is GNU PDF Ohloh page). It sees that project have steady growth and while it have not increasing year-to-year development it is not dieing out as well (which is good).
Ohloh of course is just visualization of bazaar but I believe that "a picture is worth a thousand words".