These files are optimized for the game engine to read quickly but cannot be edited in standard 3D modeling software like Blender or Object Builder. MLOD (Editable):
Run your chosen debinarizer (such as the one found in the DayZ Modding Tools suite or specialized community versions). The binarized .p3d . p3d debinarizer dayz repack
Once debinarized, open the model in Object Builder (part of DayZ Tools). These files are optimized for the game engine