Named simply 2SC3399, this 86.9 KB PDF refers to a Japanese-registered NPN transistor; the 2SC prefix under JIS indicates a high-frequency type. Although categorised as a schematic, the file is most likely the component datasheet. It is useful for confirming lead order, package outline and maximum ratings when testing or replacing the device, or when cross-referencing an equivalent. Open it with any PDF program, and confirm that the body marking and package match before trusting the figures for a repair.
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.