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There are three types of 3D objects you can create: Standard 3D objects: Objects created entirely within as 3D tool. See Standard 3D Objects. 3D Profile objects: Objects created by performing functions on 2D profile objects. See Profile Objects. Modified 2D objects. 2D objects that are assigned a thickness. See Creating 3D Objects by Editing 2D ObjectsThe way to create a 3D object is to give depth to a 2D object. This is done by opening the Properties window of a 2D object to the 3D page, and entering a thickness.
For closed 2D objects, a solid will result. You can use the Properties window to create a surface object instead. See 3D Properties.
For an open 2D object, a surface will result.
Note: The original profile can be edited (Select Edit or Edit Tool) just like any 2D object. Whatever changes you make, the thickness will remain unchanged (unless you change it).