Listed as a schematic, this 28.7 KB PDF is named only after the part number 2SC5681, which in the Japanese JIS scheme marks an NPN bipolar transistor, so it is most likely a component datasheet rather than a board diagram. The name gives no maker, package or ratings. Open it in any PDF reader to check pinout, maximum voltage and current, gain and package outline before fitting a substitute. Compare the marking on the original part with the document, since small SMD codes often differ from the full part number.
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.