ZIP archive of 6.17 MB tied to Apple logic board number 820-00239. The name gives no revision and no hint of the contents, so it may hold a schematic, a boardview or both, and should be unpacked and checked first. Such material is used to trace power rails, find test points and locate the components around a short. Apple boards carry the 820 number on the PCB silkscreen; confirm it, and the revision if one is visible, before relying on anything inside the archive.
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 @one5technology. Enginerys does not host this file.
How to open a .zip file
Compressed archive that every operating system opens without extra software.
Built-in OS tools7-Zip