RAR archive for the MSI Z370-A PRO desktop motherboard, board number MS-7B48 at revision 1.1, about 1.84 MB. MSI uses MS-7xxx codes for its consumer desktop boards, and the Z370 name points to the Intel Z370 chipset platform. The contents are not listed, so extract with 7-Zip or WinRAR and check for schematics or boardview files. These help trace VRM and standby rails, diagnose no-power faults and locate shorted components. Verify the revision printed on the PCB is 1.1, since layouts change between revisions.
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.