RAR-compressed schematic for the Gigabyte X299-WU8 motherboard, revision 1.0, about 1.75 MB. Inside should be the PDF circuit diagram for this Intel X299 board, which you extract with WinRAR or 7-Zip and open in a PDF viewer. Technicians use it to trace CPU VRM, memory and standby power rails, and to find where a short on a rail originates. Before relying on the values, check that the revision printed on your PCB is 1.0, as component choices can differ between board revisions.
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 @schematicslaptop. 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.