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The Copy Entities tools can be used on 2D and 3D objects. For the objects you want to use, be sure the Selector is set correctly (2D, 3D, or both). See 2D - 3D Selector.
These tools are typically invoked when objects are already selected. You can also invoke them even if no objects are currently selected, as long as the Select tool is active. In this case, the local menu option Select can be used to select objects to copy. Close the Select option when all objects are selected.
Local menu options:
For all of the Copy tools (except Copy in Place), the following local menu options are available:
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