This is a common part for reuse. Simply rough up the surface of the pads with coarse sandpaper or something before putting them in place to reseat on the new rotors.

That said, except when ABSOLUTELY new or freshly resurfaced there will ALWAYS be a lip on the edge of the rotor. I would NOT replace them on that indication alone. In fact unless you drive very hard in lots of in town driving, I wouldn't replace them at all. If you want to go by the letter of the specs, then put a mic on them and see just how thin they are.

Good luck,