While my friend Greg Maxey and I have similar initials, we are not the same person and it is he who is 'Greg'.
The macro Doug supplied is not compatible with the add-in process as even if it was, the macro runs before the document filename is created and thus before it is saved so it cannot reflect the name of that document in its footer.
If the aim is to add the filename to the footer then you can get the name of the document (not the PDF file) with
Code:
Sub FooterTx(oDoc As Document)
Dim i As Long
Dim fname As Range
With oDoc
Set fname = .Sections(1).Footers(wdHeaderFooterPrimary).Range
fname.End = fname.End - 1
fname.Collapse 0
fname.Fields.Add fname, wdFieldFileName, " \p", False
End With
End Sub