Small PDF reference named only by the part number 2SK2740, filed as a schematic but most likely the component datasheet for this 2SK-series N-channel FET. The name carries no further detail such as voltage rating or package. Such sheets give gate threshold, drain current, breakdown voltage and pinout, which a technician checks when diagnosing a shorted MOSFET in a PSU primary or inverter, and when cross-referencing a replacement that meets or exceeds the original specifications.
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.