MacBook Pro A1278 package for the K90I main logic board, MLB being Apple's term for the motherboard, in a 1.63 MB RAR. K90I is the internal platform code, and no 820 board number is given, so confirm the number on your PCB against the files inside. Such archives usually hold a schematic or boardview for tracing power sequencing, the SMC and charging circuits, or locating shorted capacitors. Extract it and verify the contents and revision before working on a 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 @hrtechno. 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.
7-ZipWinRARThe Unarchiver (macOS)