A schematic diagram for Apple hardware (board 820-01814). Shared as “820-01814 (SAFFORO) PDF.pdf” — a .pdf file, 11.2 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 @pkbiosbdv. 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.