Most likely your file is actually not using latin-1, yet your Emacs tries to decode it as if it were using latin-1.  Try `C-x RET r windows-1252 RET` to see if it fixes your problem.

If it does, you'll want to either add a `-*- coding: windows-1252 -*-` cookie on the first line of the file so Emacs knows how to decode it properly next time, or (the option I recommend) you can save it using another encoding such as utf-8 which has the advantage of being reasonably easy to auto-detect: with `C-x RET f utf-8 RET` you can set the coding-system to use when saving the file and then `C-x C-s` will save it using that encoding.