Add custom paper size greyed out

I'm trying to create a custom sheet size. AutoCAD help tells me to select "Custom Paper Sizes" under Device and Document Settings, but this is not an option as it is greyed out and unselectable. What would cause this? How do I make it available to select?

Thanks in advance for any help.

 

This will be greyed out for Windows System drivers, it is available only for
non-system HDI drivers.

Many Windows system drivers have provisions for creating custom paper sizes
in their Custom Properties dialogs (available in the PC3 Editor). Some HP
drivers, for example, have a "More Sizes" button, while others have an item
<<Edit Paper List>> at the bottom of the list of sizes.

"Custom Paper Sizes" under Device and Document Settings, but this is not an
option as it is greyed out and unselectable. What would cause this? How do
I make it available to select?

 

Another thing that cause it to be "grayed out" are users rights if you are
on a network or the printer was installed with users rights.

Murph