The 121 KB PDF labelled 2SC4598 sits in the schematic section, yet the name is a discrete component number, so expect a datasheet. The JIS 2SC prefix signals an NPN bipolar transistor of the high-frequency type, with no vendor or package given. A technician can use it to identify base, collector and emitter, check collector-emitter breakdown and current ratings, and compare hFE when sourcing a replacement. Cross-check the component marking first, since codes on small packages are abbreviated.
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.