ASUS X99-E WS/USB 3.1 repair guide, the RG in the name standing for repair guide, delivered as a 1.34 MB RAR archive. The board is an Intel X99 workstation model with USB 3.1 support for LGA2011-v3 processors. Guides like this describe power sequencing, VRM and memory rail checkpoints and test point locations for fault diagnosis. Its size matches another X99-E WS USB 3.1 guide archive, so the contents may be identical. Extract with 7-Zip and confirm the PCB revision.
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 @ZINFOSERVICECHANNEL1. 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.