Archive of 1.61 MB for Apple logic board 820-3172, identified only by its board number; revision, model and contents are not given. Apple uses the 820-xxxx pattern for its own boards, so match the number silkscreened on the PCB. The package likely holds a schematic PDF and perhaps a boardview for FlexBV or OpenBoardView. Use them to measure rails against expected values, trace the power-on sequence and locate test points and components when diagnosing no power or a short.
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 @Mac_Shematic_Santale. 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.