Zip package of 2.14 MB carrying the Apple board number 820-3330 and no other details. The model, year and revision are not given in the name, so check the PCB silkscreen to confirm you have the right board. Contents are expected to be schematic and or boardview material for diagnosing no-power faults, checking rail resistance to ground, tracing signals and identifying components. Schematic PDFs open in any viewer, while boardview data requires OpenBoardView, FlexBV or a comparable tool.
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.