Full documentation is available in the official PBS Pro Guides.
Currently, there is no separate documentation that is solely focused on the open source licensed version. Although these guides are focused on the commercially-licensed 13.1 version of PBS Pro, they fully document the open source licensed 14.1 version as well. The 13.1 and 14.1 versions share the same features except as noted below:
Only available with the 13.1 release:
Changes in the 14.1 release:
See the PBS Pro Roadmap for future enhancement plans.