MSI MS-6504, revision 20A, packed as a 605 KB RAR archive. No document type is given in the name, though a file of this size from MSI is most often a circuit schematic. The MS-65xx prefix is MSI's own numbering for desktop motherboards. Once unpacked, the drawings help with VRM faults, missing standby voltages and tracing clock or reset lines. Revisions of the same board can differ in parts and nets, so compare the silkscreen marking with 20A before trusting part positions or values.
The button opens the matching file on RM Schematics, or a source page if it is not catalogued there yet. The original attachment is from @IT_SERVICE_WORLD. Enginerys does not host this file.
How to open a .rar file
Compressed archive — the usual wrapper for a schematic + boardview pair or a BIOS + EC set.