Apple 820-00840-A board package, a 4.85 MB RAR archive whose name gives only the logic board number and revision A. It is identical in size to the other copies of this file and is probably the same content. Expect a schematic or boardview for the main logic board, useful for locating parts, measuring rails and tracing faults back to their source. As with any Apple board document, compare the silkscreened 820 number and revision with the file before starting the repair.
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.