Very small PDF, 94.5 KB, with the numeric name 73581 and no indication of brand, device or board number. A file this size typically holds a single datasheet, a pinout or a few pages of notes rather than a full motherboard schematic. Open it in any PDF reader to see what part it covers. Pinout and electrical tables from such a sheet help verify supply pins, enable signals and expected voltages when testing a chip in circuit, provided the exact part number printed on the package agrees.
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 @one5technology. 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.