Archive of 1.61 MB covering Apple logic board 820-2879; beyond the number, the name gives no revision, model or file list. Check that the 820 number and revision printed on your PCB match. Packages like this normally carry a schematic and sometimes a boardview, opened with a PDF reader and tools such as OpenBoardView respectively. They are used to trace main power rails, follow signal paths between chips, locate test pads and narrow down the shorted component on a dead board.
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 @Mac_Shematic_Santale. 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.