Zip archive for Apple logic board 820-00281, 2.28 MB. The name holds only the board number, without model, year or a list of files, so check inside whether you get a schematic, a boardview or both. Apple uses 820-series part numbers for its logic boards and prints them on the PCB, which is how you confirm the documents match your machine. Technicians use this material to trace power rails, find test points, locate shorted components and follow the power-on sequence. Boardviews generally open in OpenBoardView or FlexBV.
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.