PDF reference for the 2SK2551, a part named under the Japanese JIS scheme where 2SK identifies an N-channel field-effect transistor. The name gives no maker, package or revision, so those details have to be read from inside the 386 KB document. Technicians usually open a sheet like this in any PDF viewer to check maximum voltage, current and on-resistance when choosing a replacement, and to identify pins before a diode-mode or resistance test on a transistor suspected of shorting.
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.