Small 470 KB RAR archive named simply A400, with no brand, board number or content description in the name. Open it to see whether it holds schematics, a layout or firmware before planning any repair around it. Given the size, it probably contains a compact document or diagram set rather than a full service package. Confirm the model and board revision of your device match whatever is inside, and if it contains a flash image, read and back up the original chip before writing anything.
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.