A schematic diagram for Apple hardware (board 820-01700). Shared as “a2141-820-01700-x970 (1).pdf” — a .pdf file, 11.4 MB.
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 @boardviewschematicsfree. Enginerys does not host this file.
How to open a .pdf file
The standard format for schematics, block diagrams, power-sequence charts and service manuals.