Although stored as a schematic, this 409 KB file named 2SK2173 most likely contains a component datasheet. The 2SK prefix signals an N-channel FET under Japanese JIS/EIAJ part numbering; the name states no manufacturer or package. Typical uses include reading the pinout, breakdown voltage, current capability and thermal limits. That information lets a repairer test the transistor correctly and choose an equivalent that fits the same footprint and circuit stresses. Open it with any PDF reader.
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.