The name 2SC4172 is a Japanese JIS semiconductor designation, so this 109 KB PDF, though filed as a schematic, should be the reference sheet for an NPN bipolar transistor. On a PCB the part typically carries the shortened marking C4172. Repair work uses such a sheet to check pin assignment, package dimensions, breakdown voltages, collector current limits and hFE grading. No manufacturer or edition is stated in the name, so match the package and marking on the board before treating the figures as applicable or picking a substitute.
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.