Datasheet for the 2SK2043 N-channel MOSFET, with the file name stating a 600 V drain-source rating and 2 A drain current. Parts of this class commonly switch the primary winding in offline flyback power supplies for chargers, monitors and small appliances. The PDF opens in any reader and gives characteristic curves, on-resistance and package pinout, letting a technician test the removed transistor, confirm the leg order and select a replacement with equal or better voltage and current ratings.
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.