Archive named only after the Apple logic board number 820-01598, with no hint in the name of whether it holds a schematic, boardview or firmware. The 820-xxxxx format is Apple's own part numbering for MacBook logic boards, etched on the PCB, so match it exactly before use. At about 6 MB it may hold diagrams or a boardview for tools such as OpenBoardView or FlexBV. Technicians use such material to trace PPBUS and other power rails, find test points and isolate shorted components.
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 @schematicslaptop. 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.