This 96.1 KB PDF is named 2SK2161 and placed with schematics, but a part-number title like this usually signals a single-device datasheet. Japanese JIS/EIAJ designations beginning with 2SK cover N-channel FETs; no manufacturer, package or specifications appear in the name. Expect a pinout drawing, maximum ratings and characteristic tables. Use them to test the component and to confirm that any substitute has equal or better voltage and current handling. Any PDF viewer opens it.
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.