Apple logic board 820-3330 revision B, delivered as a RAR archive of about 1.97 MB. No model or content list appears in the name, so inspect the extracted files first, likely a schematic and possibly boardview data. The 820- code is Apple's PCB number, silkscreened on the board, and revision B should match your hardware. Technicians use these documents to follow rails, isolate shorts and identify components by designator during board-level repair.
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)