For Apple logic board 820-3302, this 1.81 MB zip archive bundles repair documentation, although the file name lists no model or revision. Apple 820 numbers identify the board itself, so the package likely includes a schematic and possibly a boardview. With them a technician can follow power sequencing, measure rails, find shorted parts and locate test points quickly. Extract the archive and open PDFs in a reader and layout files in a boardview program, after confirming that the PCB marking matches this number.
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 @notebookschematic. Enginerys does not host this file.
How to open a .zip file
Compressed archive that every operating system opens without extra software.