The 2SC5404 is covered by this 319 KB PDF, which the index files as a schematic. The name carries only the transistor number. A 2SC designation under the JIS/JEITA system means an NPN bipolar transistor, so the document should be a manufacturer datasheet with ratings, characteristic graphs and the mechanical outline. When a power or switching stage fails, a technician checks pin identification here before measuring junctions, and compares voltage, current and dissipation figures to choose a safe equivalent part.
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.