You can designate any user (except primary or secondary admins) as a guest. Typically, you would do this for non-employees, such as contractors or vendors.

To designate a user as a guest on Autodesk Account: Sign in, go to User Management > By User, search or select the user, click View Details, click Change Role, select This is a Guest User, and click Save. 

To remove the guest designation, deselect This is a Guest User. 

Note: Users added from a connected collaboration product are added as guests by default.