> Adobe Acrobat Reader v 5.1 vs 6 If you sometimes use Mac OS9 or Classic mode, you may want to keep your old Acrobat Reader 4.0.5 in the Mac OS9 Applications folder as the new version 6 only runs under OSX. I still have to reboot in Mac OS9 for certain applications, it and it good to have a some means of reading .pdf files.