I too had this issue with version 2013. I tried the c++ example from SolidWorks Help (http://help.solidworks.com/2012/English/api/sldworksapi/Copy_Document_Example_CPlusPlus_COM.htm). It seems that ICopyDocument only works when there is no open document. Is this normal?
Yes, it is. This is explicitly mentioned in "Remarks" section of API Help documentation:
There can be no documents open when using this method.
You might look at Document Manager analogue of this method: SwDMApplication::CopyDocument.
Application Engineer at Intercad
Tel: +61 2 9454 4444
I see... Thanks!