Fixed it myself

Dim doc As Document
Dim fld As Field

Set doc = ActiveDocument

For Each fld In doc.Fields

fld.Select
‘this is the field type, you can adjust this to suit the fields you are using, but they have to be
‘named individually, this might mean running several variations of this macro.

If fld.Type = wdFieldIncludeText Then

fld.Locked = True

End If

Next

Set fld = Nothing

Set doc = Nothing