RAR archive of 327 KB holding a boardview in BDV format for a board labelled R23-MB-D, a companion to the BRD version of the same layout. The model and maker are not given in the name, and D is probably the revision letter. BDV files are usually opened with Boardviewer-type programs, and FlexBV also reads many of them. They help locate parts, follow nets between connectors and ICs, and find test pads when measuring rails or hunting a short. Always check that the board marking and revision match the file before working from it.
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.