RAR archive of 187 KB named after Apple logic board 820-01598, with no further detail about its contents. The matching size with a known boardview for the same board suggests it holds layout data, but extraction is needed to confirm. Apple uses 820-prefixed numbers on its main logic boards, and a boardview helps find components, nets and test points during fault diagnosis. Open the contents in a boardview program and verify the board number on the PCB is identical before using it.
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.