The short answer is that a PTB file should contain everything from your company's folder except other PTB files. But there's a KB article How can I determine what files are used for what purpose in the program files and data path directory? that lists and describes each file. It will help you determine which files are critical and which ones you may be able to live without. If you find files in the PTB that aren't on this list, they are most likely non-Sage 50 files that got saved into that folder and have nothing to do with the actual Sage 50 company data.

A PTB file is really just a zip file. You can rename them and open them with any Zip utility, so I would expect any tool that repairs Zip files to work on a PTB file. Of course if the data was damaged before it was backed up, that's a different story. Then you would need to contact a Sage 50 Solution Provider (like me) to see if the data can be repaired.