I had exactly the same problem with a Word 2010 document converted from a DPF and I managed to get rid of the watermark the following way
Home
Select (far right of ribbon)
Select Objects
Delete objects
I had exactly the same problem with a Word 2010 document converted from a DPF and I managed to get rid of the watermark the following way
Home
Select (far right of ribbon)
Select Objects
Delete objects