Datasheet for the BD135 transistor in a 51.0 KB PDF, likely the same family document that also covers related types in the series. It provides the essential data a bench technician needs: pin layout, package outline, voltage and current limits, power dissipation and DC gain ranges. Typical uses include confirming a replacement part, identifying leads before testing with a multimeter diode range, and checking whether a substitute can handle the voltage in the circuit. Verify the printed marking and any gain suffix on the original before ordering parts.
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.