A 498 KB RAR archive for the ASUS B85-PLUS, an ATX motherboard built on the Intel B85 chipset for Haswell LGA1150 CPUs. The name does not list the contents, which are most likely boardview or schematic files for repair work. With such data a technician can trace the standby and main power sequence, check VRM phases and find the SPI flash. Extract the archive with 7-Zip or WinRAR, and make sure the revision printed on the board matches the documentation.
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.
7-ZipWinRARThe Unarchiver (macOS)