If you do not want to do it yourself the below link will take you to a company that will do it for you. Cheaper than buying new!

www.boggstool.com/ (http://www.boggstool.com/)

Muratic acid will work but I have not been able to get great performance from the revived files. The acid will eat away any garbage between the points and it will eat away the soft edges of the points. This greatly improves the files ability to do work but it is not nearly as good as a new file. I revive my files when they are dull and use them for softer metals like brass or mokume then eventually for lite shaping of wood or I make knives for the shop with them after they are no good as files anymore.

Not sure how the cost of shipping to a sharpening place and back plus the cost of the sharpening expense would stack up to just getting a new file.

Let us know if you try it, I would be interested in the results.