From: latitude-it.net/hp-designjet-plotter-drivers-and-windows-8/
In Autocad go into options, and then plotter setup. Follow the wizard to create a new plotter in autocad based on the HP Designjet, but as a destination select the IP for the plotter with a ‘problem’. See step by step images below starting from Options -> Plot & Publish
When in Autocad use the driver you created, when in windows use the system driver – simples!

Once you have created this on one pc the PC3 file can be copied to other machines using windows explorer. The location it needs to be copied to is –
C:\Users\%username%\AppData\Roaming\Autodesk\AutoCAD LT 2015\R20\enu\Plotters

I'm always researching questions for Designjet users everywhere...last week I set up a Designjet 500 (42") in an office and had a moment of looking less than brilliant when the user asked me to help him set up his CAD for this plotter. In all honesty I told him that I don't have any experience with CAD as I'm not a designer...and then I gracefully (I'm a princess after all!) exited his office. Now to make up for that I am posting a link to Tips and Tools for Using a Designjet with CAD.