RAR archive labelled M57-DVT-MLB, where MLB stands for main logic board and DVT for the design validation test stage, a naming style used in Apple engineering documents. The name gives no product or board number, so open the 174 KB package and identify the contents before relying on them. Small files like this are often boardviews or partial schematics. Before use, compare the 820-xxxx board number printed on the logic board with what the files reference, since part placement differs between revisions and prototype stages.
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 @cidschematicandboardviewofficial. 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.