Reference PDF for the 2SK2459N, sized 133 KB and indexed as a schematic, though the JIS-style name points to a single-component datasheet for an N-channel FET. The extra 1-5 in the name is not described and may indicate pages or a revision. Technicians open such files in any PDF reader to confirm gate, drain and source pins, the drain-source voltage, continuous current and on-resistance, all of which matter when a replacement transistor must match the original in a switching circuit.
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.