Listed as a schematic, the 307 KB PDF titled 2SK118 is by name a component datasheet for a Japanese JIS-numbered device. The 2SK series consists of N-channel field-effect transistors. The sheet supports replacement work by giving pin configuration, package outline and electrical ratings, and helps judge cross-reference parts. Markings on small packages may drop the 2S prefix or add a rank letter, so read the original carefully and choose a substitute with equal or better ratings and the same pinout.
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.