Schematic PDF whose name is only KL2D, probably a project or board code. The name gives no brand, board number or revision, so open the 979 KB document and read the title block to identify the device and the manufacturer. Once matched, a schematic like this is used to trace power rails, follow signal paths, check component values and locate the parts responsible for a short or a missing voltage. Compare the identifiers printed on your PCB with the drawing 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 @hrtechno. 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.