ADM232 document from Analog Devices, a 371 KB PDF for the dual RS-232 driver and receiver with an onboard charge pump. Filed as a schematic, it is most likely the datasheet with pinout, capacitor values and electrical limits. It helps when a serial port stops working: check the charge-pump capacitors, confirm the generated positive and negative rails, and probe transmit and receive pins. MAX232-type parts are often pin compatible, but compare required capacitor values first.
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.