I was at lockheed martin for a few years where Rational DOORS was used. Now at a smaller startup (quite happy to never touch DOORS again) I think the common an

I was at lockheed martin for a few years where Rational DOORS was used. Now at a smaller startup (quite happy to never touch DOORS again) I think the common answer is you don't use a requirements management tool, unless it's a massive system, with System Engineers who's whole job is to manage requirements. Some combination of tech specs and tests are the closest you'll get. Going back to review the original tech spec (design doc, etc) of a feature is a good way to understand some of the requirements, but depending on the culture it may be out of date. Good tests are a bit closer to living requirements. They can serve to document the expected behavior, and check the system for that behavior