Archive of high-definition photographs of the ASUS X551CA motherboard, revision 2.2 as given in the name. Board photos are useful when no boardview is available or when a technician needs to see real component placement, part markings and connector positions. They also help identify missing parts after liquid damage or bad rework. Extract the RAR with any archive tool and browse the images with a viewer. Check that the revision printed on your board matches, since ASUS often changes layouts 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 @pkbiosbdv. 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.