I used Papers 1 extensively since it came out. The authors released version 2 which is in may ways a downgrade from the old version. Many useful and easy to use features have been lost. It is very buggy. Here are some of the problems:
1. I needed use the command line and spend several hours to get it to import my Papers 1 library.
2. Matching new PDFs (which was great in the old version) has gotten very confusing and error prone
3. The software tries to be a general document manager (e.g. take care of all your presentations and Word files) but fails miserably at that task
4. Draconian and buggy license management. You may not be able to activate your license without reinstalling the operating system.

All in all an expensive "downgrade" from the old version (which I liked) and a bad user experience.

My advice: Move on to other programs such as Medelay or Bookends and don't wast your money on this one.