Zip archive of 1.48 MB for Apple logic board 820-3023, revision A, with no model named. It is expected to contain schematic and or boardview files for this board revision. Such documents are used to trace power rails and signals, read component designators and values, find test points and isolate shorted parts. A PDF reader handles schematics, and boardview files open in programs like OpenBoardView or FlexBV. Make sure the number and revision letter on your logic board match before relying on any of 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 @notebookschematic. Enginerys does not host this file.
How to open a .zip file
Compressed archive that every operating system opens without extra software.