mdt v4 can open files from previous versions, the only reason i can see wanting to save as an old file is if you are running version 4 and an older version at the same time. If you have many drawings in version 2 or above (like encampos does) you can install the 'migration assistance' tools to do batch conversions to mdt 4.0. Since i upgraded from version 1.2 I was not able to use it so cannot say if it works well or not (but the upgrade to version 4.0 was well worth it).