Yes, when you open a MacFamilyTree 5, 6 and 7 database with MacFamilyTree 8, a migration dialog will ask you, if the databases should be migrated to MacFamilyTree 8. Just confirm this dialog to automatically convert a copy of the database into the new MacFamilyTree 8 file format. If not yet there, the database will then be moved into the MacFamilyTree 8 database folder.
Databases from MacFamilyTree 4 are stored as a GEDCOM file. You can import GEDCOM files via the file menu.