The 2SK1412 is a Japanese-registered N-channel MOSFET, and this 110 KB PDF is its reference document, catalogued as a schematic. The file is larger than the LS-variant sheet, so it may include characteristic curves and package drawings along with absolute maximum ratings. Use it to identify pin order before testing the transistor with a meter in diode mode, to compare on-resistance and voltage rating when choosing a replacement, and to confirm the package outline matches the footprint on the PCB.
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.