RAR archive for the Asus K42JR laptop mainboard, revision 4.1 according to the name, most likely holding the service schematic for that board. Asus uses the model name as the board identifier, so match the model and the 4.1 revision silkscreened on the PCB before trusting it. A technician uses such a diagram to follow power rails from the charger input through the standby and CPU regulators, find the signal path behind a no-power fault, and identify the components around a short. Unpack it first, then open the PDF in any viewer.
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.