Zip archive for Apple logic board 820-00165, with the suffix a, which likely marks the board revision. At 1.35 MB it probably holds a schematic or boardview, though the name does not list contents or a Mac model. Technicians use this material to follow power rails from the input stage, locate components by reference designator and isolate shorted lines. Compare the 820 number and revision printed near the board edge with the documents, because Apple revisions can move or substitute parts.
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.