Apple logic board 820-00923 archive in RAR format, 2.28 MB. The name lists only the board number, so the exact contents are not stated, though the size suits a schematic PDF. A separate small boardview file exists for the same board, and the two are typically used side by side: the schematic shows circuits and rails, the boardview shows where parts sit. Read the 820 number on the PCB before use, because Apple boards for similar models can look alike but differ in circuit details.
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 @cyberlanelectonik. 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.