Apple 820-2883 board documentation stored as a 1.42 MB RAR archive; the name offers only the board number. Revision letter and model are absent, so compare against the silkscreen on your logic board before use. Apple-designed boards follow the 820-xxxx scheme, and each number maps to a specific design. Contents likely include a schematic PDF, readable in any PDF viewer, for tracing voltage rails, checking enable signals and locating the components involved in a no-power, no-charge or short-circuit fault.
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.