Here is a 144 KB PDF for the 2SC4728, filed as a schematic but carrying a discrete part number. In the Japanese JIS scheme, 2SC parts are NPN bipolar transistors, so the content is expected to be a datasheet with ratings, curves and mechanical drawings. The name provides no additional details. Technicians consult such sheets to verify pinout before soldering, confirm operating limits, and evaluate replacements, measuring the suspect device out of circuit to tell a shorted junction from a good one.
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.