The 2SD2079 PDF, 219 KB in size, is indexed as a schematic yet corresponds to a single discrete component. A 2SD code under Japanese JIS naming describes an NPN bipolar transistor for low-frequency applications. Expect specification tables, curves and a mechanical drawing showing which leg is base, collector or emitter. Use it when testing a suspect transistor in diode mode or when weighing an equivalent part. Make sure the abbreviated marking on the board, typically D2079, matches before trusting 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.