Catalogued as a schematic, this 179 KB PDF is named after the part number 12CWQ150FN and is most likely the manufacturer datasheet for that discrete semiconductor. The naming follows the style used by International Rectifier for rectifier diodes, so expect voltage and current ratings, pin assignment and package drawings rather than a board diagram. Repair technicians use such sheets to choose a substitute, check the forward drop with a meter in diode mode, and confirm the package marking on the PCB.
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.