Wow.
First, some caveats: there is no operating system that supports both 4 and 13, so if you want to upgrade PitStop Server you'll likely have to upgrade your OS as well. If you're running on Mac, you'll need to upgrade the hardware as well since 4 was PowerPC and 13 is (64-bit) intel.
Also, upgrading directly from 4 to 13 is not supported. You will have to recreate all hotfolders and set your preferences again. Upgrading one at a time (4 to 8 to 9 to 10 to 11 to 13) should work, but it might be better to start anew anyway.
Note that there has never been a version 5, 6, or 7.
The complete release notes are currently not available on the Enfocus website, but I can give you an overview of the most important changes.
PitStop Server 08 was a complete rewrite. The application was split into separate components running simultaneously, which allowed (among other things) taking advantage of multi-processor machines.
- Runs as a startup item on Mac OS X, service on Windows
- Simultaneous processing of multiple files on multi-processor machines
- Detailed logging
- Three different colour management engines: LittleCMS, Adobe CMM, System CMM
- Process folder hierarchies
- File renaming options
- Hot folder locking
- Import and export of hot folders
PitStop Server 09
- Greatly improved processing speed
- CLI to process files from the command line or through scripts
PitStop Server 10
- Transparency flattening
- Black Point Compensation
- New XML reports
- Annotated PDF reports
PitStop Server 11
- Smart Preflight: use variables from XML or JDF tickets to control processing
PitStop Server 12
https://www.enfocus.com/en/support/know ... 000jfcpIAA
PitStop Server 13
https://www.enfocus.com/en/products/pit ... -server-13
Of course each version also updates the compatibility with new PDF features, PDF/X and GWG versions, and each is compatible with Action Lists and Preflight Profiles created in the corresponding PitStop Pro version, which means they also have all new checks and fixes added in those versions. At quick estimation suggests over 100 new actions have been added, some of which may be very interesting - for example add bleed, gather ink information, detecting printer marks, ...