The name of this 238 KB PDF consists solely of 2SC3425, a JIS designation for an NPN bipolar transistor. Although catalogued as a schematic, it is most likely the part's datasheet. Typical uses include verifying the collector, base and emitter order, checking breakdown voltage and maximum current, and reviewing the outline drawing so a replacement fits the board. Any PDF viewer opens it. Match the code printed on the component and any suffix letter before swapping parts.
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.