I have sharpened double-tooth saw blades using a feather-edge file of the appropriate size. This includes pruning saws, swede saws, and SWAK saw blades. Some of the newer ones with induction-hardened points would require diamond abrasive to sharpen effectively.

The saws I sharpened showed some improvement. If you have to take off a lot of metal, though, you start to lose the set of the teeth that creates a wider channel (kerf) that keeps the blade from binding in the cut. Generally, nothing cuts as well as a new blade.