Schematic in PDF for Apple logic board 820-00165-A, a 1.54 MB document; the name gives no Mac model. Apple numbers its logic boards in the 820-xxxxx format, with the trailing letter showing the revision. Schematic pages let you follow power rails, enable signals and the power sequence, identify components by reference and work out which circuit fails. Read it alongside a boardview for the same number, and verify that the 820 number printed on the PCB matches before trusting values or net names.
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 @lappysan. 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.