At 153 KB, this PDF named 2SC4399 is presumably the datasheet for that NPN bipolar transistor, even though the index lists it as a schematic. The 2SC designation comes from the JIS standard for NPN devices of the high-frequency class. No other information is encoded in the name. Technicians typically consult such a document to identify leads with a multimeter in diode mode, compare ratings when sourcing an equivalent and read the package dimensions. Confirm the marking on the actual component matches first.
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.