There is only one file type that uses the .MPM extension:
Max Payne Modfication File
Compressed Max Payne game modification file created using the Remedy Archive System (RAS); used for modifying existing Max Payne levels or creating new custom levels; can be applied to the Max Payne application using the RASMaker program.
Max Payne 2 mod files use the .MP2M file extension.
Updated: August 24, 2014