Updating a custom property in the header

[JonFleming]

I'm working on a macro for a document to submit to the FDA. There's a bunch of items that appear many many times in the document and change when you start a new document. There's also a bunch of technical reasons why plain search and replace doesn't work and takes along time to fail.

So I've defined a custom property for each of these items. There's a table at the beginning of the document with the property names in the first column. The user fills in the second column with the desired value. My macro extracts the information from the table and changes the property value, turns off screen updating, then updates all instances of the property:

Sub UpdateSpecificPropertyFields(FieldName As String)
    Dim pRange As Word.Range
    Dim oFld As Word.Field
    For Each pRange In ActiveDocument.StoryRanges
        Do
            For Each oFld In pRange.Fields
                Select Case oFld.Type
                    Case wdFieldDocProperty
                        If InStr(oFld.Code.Text, FieldName) Then
                            oFld.Update
                        End If
                    Case Else
                       'Do nothing
                End Select
            Next
            Set pRange = pRange.NextStoryRange
        Loop Until pRange Is Nothing
    Next
End Sub

But the instances of the property in the header do not get updated. Help?