Compressed boardview for the ZH6-MB-D board, packed as a 108 KB RAR, with MB most likely meaning mainboard and the D suffix a variant, while the device model and maker are not stated. After extraction, open the layout in OpenBoardView, FlexBV or a comparable viewer to find components, pins and net connections. It is handy for following rails back to a short and locating test points. Check the board marking and variant on the PCB first, since variant layouts can differ.
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.