RAR archive of 1.66 MB for Apple logic board 820-3302, with no revision, model or contents indicated by the name. The 820-xxxx number is Apple's own board identifier and is printed on the PCB, so that is what to match. Inside you can expect a schematic and perhaps a boardview for OpenBoardView or FlexBV. Technicians use these to measure rails against expected values, follow enable and power-good signals and pinpoint the component pulling a supply to ground.
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.
7-ZipWinRARThe Unarchiver (macOS)