Boardview for Apple logic board 820-4652, stored as a 429 KB RAR archive; the name gives only the board number. Apple uses the 820 prefix for its logic boards, and other files in this set tie this one to the A1416 model. Opening it in OpenBoardView, FlexBV or a similar viewer lets you locate components, follow nets and probe test points when tracking down shorts or missing power rails. Check that the board number and revision suffix on your PCB match before relying on layout positions.
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 @schematicslaptop. Enginerys does not host this file.
How to open a .rar file
Compressed archive — the usual wrapper for a schematic + boardview pair or a BIOS + EC set.