Preferred width is a cell property, so you need to apply it to the cells of the table, as below. I have not checked the rest of your code.
Code:
With wdDoc
For Each pT In wdDoc.Tables
pT.Range.Cells.PreferredWidthType = wdPreferredWidthAuto
pT.Range.Cells.PreferredWidth = 0
Next
End With