Named 2SK3491, this 29.8 KB PDF is most likely the datasheet for that JIS-numbered device, despite being listed as a schematic. A 2SK designation identifies an N-channel field-effect transistor. The practical value lies in confirming pin assignment, package and ratings when diagnosing a shorted FET or choosing an equivalent. Markings on surface-mount packages are often shortened, so match the digits carefully, verify the footprint on the PCB, and take antistatic precautions while fitting the new 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.