ZIP archive of 3.23 MB for the ASUS X451MA, with no further details in the name about revision or contents. The size matches the other X451MA BIOS packages, so it most likely holds a flash image, though that should be confirmed after extraction. Inspect what is inside before use. If it is a BIOS, back up the original chip with a programmer, confirm the image size matches the chip, and check the board revision silkscreened on the PCB.
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 .zip file
Compressed archive that every operating system opens without extra software.
Built-in OS tools7-Zip