Try something like:

Sub ScratchMacro()
Dim oFld As Field
DocUnprotect
For Each oFld In ActiveDocument.Fields
If oFld.Type wdFieldFormTextInput Then
oFld.Unlink
End If
Next oFld
DocProtect
End Sub

Sub DocUnprotect()
On Error Resume Next
ActiveDocument.Unprotect
End Sub

Sub DocProtect()
On Error Resume Next
ActiveDocument.Protect Type:=wdAllowOnlyFormFields, NoReset:=True
End Sub