Small 136 KB RAR archive named for the N55SF mainboard, revision 2.0, with MB indicating motherboard. The name does not say whether it holds a boardview, schematic or firmware, but the compact size is typical of boardview layout data. Extract it to see the contents before use; boardview files open in OpenBoardView or FlexBV and help locate components, test points and nets when diagnosing shorts or missing rails. Whatever is inside, verify the revision printed on the PCB matches 2.0 before relying on it.
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 @cyberlanelectonik. 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.