Flash MX 2004.
library.duplicateItem( [ namePath ] )
namePath A string that specifies the name of the item to duplicate. If the item is in a folder, you can specify its name and path using slash notation. This parameter is optional.
A Boolean value: true if the item is duplicated successfully; false otherwise. If more than one item is selected, Flash returns false.
Method; makes a copy of the currently selected or specified item. The new item has a default name (such as item copy) and is set as the currently selected item. If more than one item is selected, the command fails.
The following example creates a copy of the item square in the library folder test:
fl.getDocumentDOM().library.duplicateItem("test/square");