Small 35.2 KB PDF identified only by the part number 2SK665, a designation from the Japanese 2SK family of N-channel FETs, so the content is most likely a component datasheet rather than a full circuit diagram. It should give the pin layout, maximum ratings and typical electrical characteristics. Use it to confirm which leg is gate, drain and source, to test the transistor with a diode-mode meter, and to compare figures when searching for a cross-reference replacement part.
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.