ZIP archive of 1.55 MB named after X751LKB, which follows ASUS laptop naming, although no brand is given and the name does not say what is inside. It may hold a schematic, boardview or firmware for that model, so extract it and check the contents before use. Whatever the archive holds, match the board name and revision on the PCB against the files, and if it contains a BIOS dump, back up the original SPI chip with a programmer 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 @notebookschematic. 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