PDF reference sheet for the 2SC3921, 30.7 KB, catalogued among schematics but named with a JIS transistor code. A 2SC prefix in that system identifies an NPN transistor, usually intended for high-frequency circuits, so this should be a concise datasheet. Expect pin configuration, ratings and a package outline. Use it to identify collector, base and emitter during in-circuit testing and to choose a replacement with equal or higher voltage and current limits. Check the body marking matches before relying on it.
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.