RAR archive for the Apple MacBook Air A1465, logic board 820-3435, following Apple's own 820- part numbering for main boards. With a size of 1.35 MB it most likely contains schematics or boardview data for this board. Technicians use these to follow power rails, locate components and test points, and narrow down a short circuit. The name gives no revision letter, so read the full number on your PCB and confirm it matches 820-3435 before relying on the document.
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.