Named simply 18TQ, this 180 KB PDF is catalogued as a schematic but appears to cover a component series rather than a board, since no voltage suffix, model, board number or revision is given. The prefix follows the International Rectifier style used for Schottky rectifier families, so the document probably summarises several voltage grades in one datasheet. Technicians open it in any PDF viewer to choose the correct grade for a replacement and should match the full code on the original part before soldering.
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.