Perhaps DDE Links do not work in docx, but here’s what I’m doing. Open document, go to another document, highlight all text, copy, go to another document in the same drive, Paste Special DDE Link, OK. The doc is pasted in, go to Edit/External Links and the link is present. Click anywhere in the pasted text and go back to Edit/External Links and it is now greyed out. But try and edit the pasted text and you get Write Protected No Modifications Allowed, but there is no way to make the text unprotected, so where is it getting protected? Go to the original doc, make a change, click Tools/Update All, go back to the destination doc, confirm that Edit/External Links is still greyed out, click Tools/Update All and unsurprisingly nothing happens.
Hope this makes sense. Am I missing something?