For the 2SC4679, this 224 KB PDF is listed as a schematic but named after a single semiconductor. JIS/JEITA numbering uses 2SC for NPN bipolar transistors, so the document should contain datasheet information: ratings, characteristic curves and package outline. The filename carries nothing else. Repair technicians rely on it to identify pins, verify operating limits and select an equivalent replacement, checking footprint and ratings so the substitute survives in the original circuit.
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.