Compressed RAR file, 1.34 MB, covering Apple logic board 820-2494. Only the board number is present in the name, so the Mac model, revision and type of documents inside are unknown until extraction. Apple marks its logic boards with these 820 part numbers, and matching them is the first check before trusting any drawing. A schematic supports tracing rails and signals and checking where a short originates, while a boardview viewer such as OpenBoardView shows where each component and test pad sits.
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.