PDF schematic for the Apple logic board 820-02536, a companion to the boardview file for the same number. It holds the full circuit diagram: power rails, the sequencing logic, the SMC and the charging circuit, along with the net names used for fault finding. The 820 prefix is Apple's internal board numbering, and one model may use several different boards, so confirm the number etched on the PCB. Use it together with the boardview to turn net names into physical locations while measuring voltages.
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 @notebookschematic. 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.