This is within the Autocad Print Window. Before you set the Printer to the
default Windows Printer you need to be sure that the Adobe Acrobat printer is
the default in windows.
Right click on the Acrobat PDFWriter print driver and set it to default.
In Autocad choose File Print
Set device and default selection to - Default System Printer
Click on the button - Pen Paramaters
Hold down your shift key and click first on Color #1 then scroll to the end
of the list to Color #255 until all of the choices are highlighted.
In the window to the right - change the Pen number shown to 7 and hit the
enter key. All of the Pen numbers should show #7 as the pen color.
Finish plotting in the usual manner - the resulting plot will be saved in PDF
format and in black lines.
Let me know if this works for you. I was using Rel 14 for this.