Labelled 2SC5256, this 165 KB PDF most likely contains the datasheet for that JIS-coded NPN transistor; an FT-suffixed variant document also exists. It names no board or appliance. Content of this kind normally includes maximum ratings, electrical characteristics, typical performance curves and package information. Technicians use it to identify leads correctly, read marking codes and compare specifications when looking for a replacement transistor that fits both the footprint and the electrical demands.
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.