Second copy of a RAR archive for the Apple 820-00840 board, revision A, with the same 4.85 MB size as the other package, so it is probably a duplicate. The name does not list the contents, which for Apple board packages are typically schematic and boardview material. Open it with a RAR extractor and compare against the other copy before keeping both. As always, the 820 number and revision on the logic board must match the documents before you use them for diagnosis.
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 .rar file
Compressed archive — the usual wrapper for a schematic + boardview pair or a BIOS + EC set.