RAR archive, roughly 735 KB, named after the ASUS P9X79 motherboard, with no revision or content type stated. Extract it with 7-Zip or WinRAR and inspect the files to learn whether it contains boardview, schematic or other service data. Material like this helps locate parts, trace CPU and memory power rails, follow standby and power-on signals and find shorts. Note that PRO, DELUXE and LE variants of this board exist with different layouts, so make sure the documents match the exact model and revision on your PCB.
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.