With only 11 posts under your belt Old No7, you haven't been around long enough to know that rocky mtn bill isn't going to like your pro-2nd Amendment tagline. He loves to bash Donald Trump and our NRA.
To answer your question, this process is simply a weak acid pickling. Most white vinegar is diluted to 4 to 5% acetic acid. Like any acid pickling process, heat will accelerate the process.
It will help to scrub your files in a detergent first to remove any oils and built-up chips so that the acid can eat at the steel more evenly. The time of the acid pickle depends upon strength of the acid, temperature, and how dull your files are to start with. When they are sharp, rinse, dry, and spray with a light oil or rust preventive.
I find that the "Works Toilet Bowl" cleaner is better than vinegar. It is cheaper to use because it is 9.5% Hydrochloric acid, which can be used full strength for a shorter interval, or diluted about 50-50 and used for a longer interval. Hardware store also carry Muriatic acid, which is also a dilute Hydrochloric acid. Use rubber gloves and avoid getting it on your skin. Don't get household bleach anywhere near it because Chlorine gas will be formed. I once saw a source that said the "Works Toilet Bowl Cleaner" contains bleach and hydrochloric acid. That is proof that you should not believe everything you read on the internet. That mixture could damage your lungs.
Acids like hydrochloric or acetic can be re-used until they are depleted. When they no longer have enough bite to sharpen files, they will still work as a mild rust remover. They start working slower and slower until they just don't work.
