An easy 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 (see Object Properties) 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.
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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).
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