ZIP archive for the Apple logic board 820-3536, about 1.5 MB. Apple uses 820-xxxx numbers silkscreened on the board to identify the logic board, which is more precise than the model name; the specific Mac model is not given. The contents are not described, and a file of this size may contain a schematic, boardview or firmware. Technicians use such files for tracing rails, locating components and diagnosing shorts on MacBook boards. Confirm the 820 number on your board matches 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 .zip file
Compressed archive that every operating system opens without extra software.