Is there a (free) PDF reader that could restore last viewed page when opening a PDF in OS X 10.10?
Preview can do it. Just be sure that in your Preferences → PDF tab, you have checked the following option:
And if you have to resave the file (for whatever reasons), use Adobe Reader, which provides the same functionality.
Note: Preview.app can seriously mess up the internal structure of a PDF, so that it is no longer usable.