Compact RAR archive, 187 KB, tied to Apple logic board 820-01598. The name gives no hint of what is inside, but at this size it most likely holds a boardview or a small firmware image rather than a full schematic set. Apple stamps its 820-xxxxx number on the main logic board, so read the silkscreen and confirm it matches before using the contents. Boardview files open in tools such as OpenBoardView or FlexBV and help locate components, test points and nets when chasing a short or a missing power rail.
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.