At 411 KB, this PDF for the 2SC5717 is one of the larger documents in the set and is probably a complete datasheet with graphs. The JIS 2SC prefix means an NPN bipolar transistor; the name tells nothing more. Technicians consult such sheets to identify terminals, check breakdown voltage and collector current, and judge whether a common substitute will survive in the circuit. Always read the marking on the actual part, because abbreviated codes on small packages can be ambiguous.
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.