Here the 2N4123 is covered by an 83.6 KB PDF, the plain-named version alongside an RE-suffixed file for the same number. Despite the schematic label, it is best treated as a component datasheet for a JEDEC-registered part. Repair technicians use such sheets for identifying leads before in-circuit diode tests, checking ratings against the circuit's supply voltage, and finding equivalents. Make sure the package on the PCB matches the outline in the document, as pin order can vary between case styles.
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.