A compact 75.6 KB PDF indexed as a schematic but named 31DQ09, a code that looks like a rectifier diode part number, not a motherboard. Expect a component datasheet describing one device rather than a full circuit. Datasheets like this help when a diode in a supply or protection path has failed: they give forward voltage, reverse rating and package outline so a suitable substitute can be chosen. Check that the marking on the original component matches this number exactly, as the trailing digits usually encode the voltage class.
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 .pdf file
The standard format for schematics, block diagrams, power-sequence charts and service manuals.