Archive for the Apple logic board 820-2936, revision A, judging by the name, likely holding the schematic or boardview set. Apple identifies its logic boards with 820-xxxx numbers printed on the PCB, and the same model can use different boards, so always read the number off the board itself. The 1.74 MB RAR suits a schematic PDF. Such files are used to follow PP rails from the charger through the power sequence, check SMC signals, find shorted capacitors and locate components for microsoldering repairs.
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 @cidschematicandboardviewofficial. 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.