Filed under schematics, this 209 KB PDF is named after the part number 2SC3405, which follows the Japanese JIS scheme where the 2SC prefix marks an NPN bipolar transistor intended for high-frequency use. The content is most likely the component datasheet rather than a board diagram. Technicians open it in any PDF reader to check pinout, package outline, maximum ratings and hFE grading before fitting a substitute. Confirm the marking on the actual part matches, since SMD codes are often abbreviated.
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.