Don't get hung up on direct output to the plotter. Just get your art work (even letters) to a file in HPGL format. You might look into HPGLdistiller pldaniels.com/hpgl-distiller/ to clean up and simplify any files generated by "complex" graphics software.
Files can be sent to the plotter via a terminal window. "Command prompt" from windows
(copy <directory directory file.name> com1 etc. This is all DOS technology remember ;-). Make sure of your handshake, use Xon/Xoff, depending on the serial cable you get. (Check the connections part of the manual).