Indexed under schematics, this 83.0 KB PDF is named 12tts08, a code that resembles International Rectifier or Vishay thyristor (SCR) part numbering. If so, it is a datasheet giving gate trigger current and voltage, holding current, blocking voltage and on-state current, plus package pinout. These parts are often used for inrush limiting and crowbar circuits in power supplies. Confirm the marking on the installed device and the pin order, since gate, anode and cathode positions vary between packages.
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.