The 2SK657 datasheet, filed as a schematic, is a 35.7 KB PDF; the 2SK prefix identifies an N-channel FET in the Japanese semiconductor numbering scheme. Expect pinout, ratings and characteristic data on a page or two. In repair work it helps when a transistor in a power or audio stage has failed: confirm gate, drain and source, compare maximum voltage and current, and find a substitute. Verify the printed marking on the component matches before trusting the figures.
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.