RAR archive for the ASUS Sabertooth Z87 motherboard, 311 KB, with no hint in the name about what it contains. At this size it is probably boardview or schematic-type material rather than a firmware image, so inspect it first. Such files let a technician find components by reference, follow net connections and pick test points while chasing a short or a dead rail. Match the board revision silkscreened on your PCB to the document before trusting positions or values.
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)