Revision A documentation for Apple logic board 820-3209, packed into a 2.71 MB zip. The device model is not stated in the name, so identify the machine by the board marking. The archive likely holds a schematic and possibly boardview data, which technicians use to trace power rails, check voltages during power-on, locate components and test points and isolate shorts. Open diagrams in a PDF viewer and layout files in OpenBoardView or FlexBV, and confirm the revision letter matches your PCB first.
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.