A 1.32 MB PDF schematic labelled UL20A, a notebook model code; the name does not include a brand, board number or revision. Read the first pages for the project name and confirm it against the number silkscreened on the motherboard. Schematics like this are used to follow the power-up sequence, measure expected voltages, check enable and reset lines, locate the BIOS flash, and identify parts connected to a rail that measures low resistance to ground. Searchable text makes net lookups quick.
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 @alischematics. 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.