Apple schematic in PDF format for logic board 820-00840, revision A, about 6.68 MB in size. Any PDF viewer opens it, and the text search helps to jump between net names when following a power rail or signal across sheets. Technicians use these pages to find what feeds a dead rail, which components sit on a shorted line and how the power sequence is meant to run. Make sure the board number and revision printed on your PCB match before trusting values or part placements.
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 @one5technology. 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.