A 200 KB PDF for the 2SC5458, a part in the Japanese 2SC numbering scheme for NPN bipolar transistors, filed here as a schematic. The content is almost certainly the device datasheet, with ratings tables, typical performance curves and the package outline. It is useful for locating the correct pins, confirming that a replacement is suitable and understanding the device limits when diagnosing a failed stage. Compare the printed code on the original part with the sheet before ordering anything.
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.