RAR archive of 536 KB for the MSI MS-6505 motherboard, marked REV 100 in the name, which most likely refers to revision 1.00 though that reading is not certain. The name does not say whether it holds a schematic, BIOS or other service data, so unpack it with WinRAR or 7-Zip and inspect. MS-6xxx is MSI's own board numbering. Verify the code and revision printed on the PCB before relying on the contents, and back up the existing BIOS chip before flashing any image.
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.