A short 46.2 KB PDF named 2N6668, indexed as a schematic although its title is only a JEDEC discrete semiconductor number. No host device or board is given. A file this small is likely a concise datasheet covering ratings, key characteristics and the case outline. Technicians use it to confirm pinout before in-circuit testing and to check a replacement's suitability. Match the package and marking on the component, and ensure the substitute's voltage and current ratings are at least equal.
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.