A 266 KB PDF named for the 2SC3074 part, listed in the schematic category, though its content is most likely a transistor datasheet. JIS numbering assigns 2SC to NPN bipolar transistors in the high-frequency class. A technician would rely on it for terminal identification, rating tables and package dimensions when diagnosing a failed stage or choosing an equivalent. Any PDF reader opens it. Check that the marking on the real component, including gain suffix, matches this number.
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.