The last version to open v.3-5 files was FreeHand 8. Whereas FreeHand 7 files should open in FHMX.
Obviously, old files need to be opened and saved as a newer version so get FH8 and install. In Windows it works as legacy and on Mac you will need to use Sheepshaver and install OS9. Is it worth the trouble?
Btw, old Mac versions of FreeHand are here: http://macintoshgarden.org/search/node/FreeHand