RAR archive of 2.09 MB for Apple board 820-3298, revision A, with D8 in the name, probably an internal project code, though the name does not confirm it. Model and contents are not listed. Match the 820 number and revision on the PCB first. A schematic from this package lets you trace rails from the DC-in and charger through the main regulators, while a boardview, if included, opens in OpenBoardView or FlexBV to locate parts and test points quickly.
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 @Mac_Shematic_Santale. 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.
7-ZipWinRARThe Unarchiver (macOS)