RAR archive for Apple board 820-3437, around 1.39 MB, with no model, revision or content details in the file name. It likely carries schematic pages for the logic board, viewable in a PDF reader after extraction. Apple labels each PCB with its 820- number, so verify the marking and revision letter on your board before relying on the drawings. Technicians use these to follow power rails, find test points and pinpoint failed components during diagnostics.
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)