You may create exact copies of the selected document(s) of a specific document type.  

To change the Document group 1 or 2 on documents: 

1.On Documents (Documents list) (Action ribbon), select the Document type, if the correct document type for sales documents (i.e. Invoices, Credit notes or Quotes) or purchase documents (i.e. Purchases, Supplier returns or Orders).

2.Select the Document(s), right-click on Documents → Copy document on the context menu. Exact unposted copies of the selected documents will be created for the same document type.

If you need to select multiple documents, press the Ctrl or Shift key and click on each document, which you need to copy.

Once this is done, you may edit / post these documents.