Archive named for the P8H61-M2 USB3 desktop motherboard, the H61 chipset variant with added USB 3.0, though the name does not say which repair document it contains. At 204 KB it is probably a boardview or small schematic rather than firmware. Open the RAR and check the format inside before choosing a program. The USB3 version differs from other P8H61-M2 variants in parts around the extra controller, so check the exact model string and revision on the PCB before using any component location.
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 @boardview. 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.