Filed among schematics, this 467 KB PDF carries just the transistor number 2SC4320 and should be regarded as its datasheet. By JIS designation 2SC means an NPN bipolar transistor, often marked C4320 without the 2S. The content is used to determine base, collector and emitter positions for the given package, to read absolute maximum ratings and characteristic curves, and to judge whether an alternative part will survive the voltages and currents present in the circuit being repaired.
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.