This 180 KB PDF, named 30L30CT, is labelled a schematic but follows a discrete semiconductor part-number style; the CT ending is often used for dual common-cathode rectifiers, though the document itself should be checked to confirm. Expect a datasheet with ratings, characteristic curves and a package outline. Technicians use it to verify which pins are anodes and which is the shared cathode before replacing a part in a power stage. Match the full marking on the PCB component before trusting the figures.
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.