Small 99.1 KB RAR for Apple logic board 820-00165-A, project J113, marked MB for main board. The modest size suggests a boardview file rather than a full schematic, though the archive should be opened to confirm. Boardview layouts let a technician locate components, nets and test points while probing for shorts or missing voltages, using viewers such as OpenBoardView or FlexBV. Apple 820-xxxxx numbers identify the logic board, so match the marking on the PCB before relying on part placement.
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 @SCHEMATICWORLD. 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.