A small 98.7 KB PDF about the 2SK1416, catalogued under schematics but most likely a component datasheet. In JIS numbering, 2SK marks an N-channel FET, while maker and package are not stated in the name. The document can be used to read pin order, absolute maximum ratings and on-state characteristics. Those details guide short testing, cross-referencing to an available equivalent, and confirming that the code on the physical transistor matches before you trust the data.
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.