You can remove rust from sword/knife blades in a variety of ways. You
cannot remove pits because the original blade material that was in the
pits is now gone.
I found the following article on the web to be very thorough, from a
sword dealer no less:
The fifth paragraph in the article goes over rust removal on steel
Basically, you do not want to scratch the blade... so you will need to
use a chemical treatment (DO NOT SAND OR SCRATCH OFF THE RUST). They
recommend CLR (Calcium, Lime, Rust), which you can find at just about
any hardware store. This product removes rust from surfaces. Once all
the rust has been removed (this can take a while), be sure to coat the
blade with a high quality acid-free oil (like high quality gun oil).
I hope this answers your question, be sure to ask for a clarification
if you need one. Also, I urge you to follow the link below in the
section labeled "search strategy" for LOTS of additional information.