When you say "random" do you mean the tool don't always hang with same files? One time run correctly on a particular file, and next time fail with that same file?
If yes, it's not an usual situation, but it's possible if cumulative errors bug is involved and you are running the tool on more than one file at a time, so try to identify the sequence of PDF's that produce that problem.
If no, and you are able to clearly identify a PDF file that always make the tool fail, please email it to me so I can check for what's wrong.
Program is not hanging on purpose, it's just bad code (bug) that's producing that behavior, most probably because of some specificity of the PDF files your are testing on, but I need to debug with these files to be able to fix it.
And yes, hanging all program because of a tool incompatibility with a particular file is wrong, and you can be sure current code try to prevent it, but definitively something is not working, how it's supposed to work, with your files, so I really need your help on this.