Well you asked a very good question, everything or every information is avaialble in the proe documentation you recieve with pro/engineer software.
The trail files are generated in commercial versions only, and can be read in the commercial versions only.
Trail files are generated for every instance that you use the pro/engineer software, they are design specific files that tells you everything you did. it is a sort of script files. with these you can design templates and customise them specific to your company and in config file you can tell software where to store them for troubleshooting purpose. i always store them in different folder that i have specified in config.pro.
you can have a look at the scripting of the files by opening them with text format and see the various changes, that follows your specific design routines in that special intance of the pro/engineer session, that how you controlled the design.
well i must say it is very good tool in case of accidental crash, to backup data, to customise the design and design variable.
to look at the file first create the part in proengineer and then quit. the specific trail file it created rename it to something else and try to play it in another session of proengineer, you will see the every step you followed to make that design. itis quite facinating sometimes.
here i could tell you only this info, if you want more then you will find this info in any good proenginner book or its documentation.
good luck.
