As you may have noticed by now: Current (2014) Autodesk software can't do much with MDT files (even though they are confusingly called DWG).
Inventor requires you to have MDT installed to be able to do anything with MDT files... which is useless to the max: then you may as well just use your MDT install.
AutoCAD tends to just disable all commands (except save... which is useless in a larger extend: why would you want to save if you can't do anything else?)
But! DraftSight (free/spamware AutoCAD clone) will just open MDT files and let you save them as anything else... Autodesk software will then complain about the non-Autodesk origin of the file... but that is less of a problem then the actual Autodesk origin of the file (=MDT).
Just as a workaround... until Autodesk actually enables its software to open Autodesk files.
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