Apple logic board 820-2828 archive, RAR format, around 1.93 MB. The name offers nothing beyond the board number, so model, revision and document types are unknown until it is unpacked. Apple prints 820-series part numbers on its boards, and a technician should confirm that marking matches before using these files. Typical contents are a schematic for tracing voltage rails and signals and sometimes a boardview for finding component locations, test points and the area around a suspected short.
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.