From the Windows Start menu, choose Settings → Printers. The Printers window lists all the printers that are set up for your computer.
Select the printer whose print driver you want to use. This selection is important, because even though you will not be printing to this printer, you will be using its print driver. The print driver determines things like fonts and available page sizes, so choose one that is appropriate for what you are printing. As desired, you can also create a copy of a desired printer specifically for the process to follow.
Do one of the following:
Choose File → Properties, or,
Right-click the printer and choose Properties, or,
Double-click the printer name and choose Printer → Properties.
Click the Details tab.
From the Print To The Following Port list, select FILE and choose OK.
The next time you print to this printer you will be prompted for a file name.
Specify the file name and the location.
The active drawing prints the file you specify using the selected print driver.
Most of the time a .plt and a .prn are just extensions given to the hpgl data that would normally be sent to a pen plotter. Just writing an (hpgl) plot to a file with that extension should be enough.
As excerpted on July 11, 2008, from http://www.cadalot.co.uk/icad/tipstricks.htm#Printing.