Archive of service data for an Apple MacBook built on logic board 820-1889, with the internal project code M42B noted in the name. Apple stamps the 820-xxxx number on the PCB itself, so a technician should read that marking and confirm it matches before using the material. Such archives usually hold a PDF schematic and sometimes a boardview, which together let you follow power sequencing, check for shorted rails and find components around the charger and CPU sections. Extract with any RAR-capable tool such as 7-Zip or WinRAR.
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 @generalschematics. 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.