ASUS B150-Plus motherboard repair guide, a 1.25 MB RAR archive. A technician would consult it to verify power rails in the correct order, find where startup stops and target parts known to fail. Note that a separate 1.42 MB B150-PLUS guide and a D3 variant also exist, so the contents may differ; compare against the board actually being repaired, including its printed revision. Open with any RAR-capable extractor; the documents inside are not listed.
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.
7-ZipWinRARThe Unarchiver (macOS)