Compact RAR archive of 142 KB named A840-mb-d, where mb most likely stands for mainboard. No brand or revision is given, and the trailing d is not explained by the name, so treat the contents as unconfirmed until extracted. A file of this size might hold a small schematic or board layout file for an A840 device. Check that the model on the hardware matches before using it to trace power rails, locate components or test points and diagnose a short.
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 @cyberlanelectonik. 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)