Reference document for the 2SC1815, a 310 KB PDF classed as a schematic. In JIS numbering the 2SC prefix denotes an NPN bipolar transistor, and the file is most likely its datasheet with pinout, outline drawing, absolute maximum ratings and gain grades. No manufacturer is named, and separate editions of this number exist in the index, so compare package and marking with the actual part. Technicians use it to test junctions, confirm the collector lead and pick a replacement with adequate voltage and current ratings.
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.