Datasheet PDF for the 2SD1979, filed under schematics at 42.4 KB. The 2SD prefix follows JIS convention for NPN bipolar transistors of the low-frequency class, and the E suffix in the name is undefined. A compact document like this usually gives maximum voltages, collector current, power dissipation and the lead order. Technicians need that before desoldering a suspect device, testing its junctions with a multimeter or deciding whether a cross-reference part is a safe swap.
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.