RAR archive for the K40AB board at revision R1.2, 1.25 MB in size. The name does not say whether it holds a schematic, a boardview or both, though the size suggests schematic content. Technicians use such files to trace power rails, follow enable and power-good signals and locate components while repairing no-power or no-boot faults. Extract it and open the contents in the matching viewer. Check that the PCB marking shows revision 1.2, since other revisions may differ in layout and parts.
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 @cyberlanelectonik. 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.