PDF schematic whose name gives only QK1 with an A suffix, which may be a project code and revision, though no maker, brand or board number is stated. At about 3.1 MB it is likely a full motherboard diagram set. Such files are used to trace power rails, follow the power-up sequence, read connector pinouts and locate the components on a shorted line. Since the identifiers are minimal, open it first and check the board code shown in the title blocks against the silkscreen on the PCB before relying on it.
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 @ITHINKHS. 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.