Designation 2SC3457 is all the name reveals about this 116 KB PDF filed under schematics. Under Japanese JIS numbering a 2SC part is an NPN bipolar transistor, so the content is most likely its datasheet with electrical characteristics and package dimensions. Such a reference helps when replacing a shorted output or switching transistor, confirming lead order and making sure a substitute handles the same voltage and dissipation. Verify the case style physically before soldering anything in.
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.