Combined datasheet PDF of 210 KB covering the 4N25 to 4N28 and 4N35 to 4N37 optocouplers, although indexed as a schematic. These are well-known phototransistor-output optoisolators widely used for feedback in switching power supplies and for signal isolation. The sheet gives pinout, current transfer ratio, isolation voltage and LED forward ratings. Technicians use it to test a suspect optocoupler, confirm which part numbers are interchangeable and check pin order before fitting a replacement in a PSU or charger circuit.
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.