The following code will add a { DOCVARIABLE varname } field to the Primary
Header of the First Section of the active document.
You probably need to be more specific about just where in the Header it gets
added and you will have to do that by setting varange appropriately:

Dim varange As Range
Set varange =
ActiveDocument.Sections(1).Headers(wdHeaderFooterPrimary).Range
ActiveDocument.Fields.Add Range:=varange, Type:=wdFieldDocVariable,
Text:="varname"

Just for more information, here is the code I have.  I am not getting errors
on the docvariable.add lines, but I am also not seeing the variables in the
document (anywhere).  Also, I am trying to do this from Access.

Dim oApp As Object
Dim oDoc As Object
Dim CurrDate As Date
Dim strSavDir As String

If (strApp = "Yes") Then
'add check for existing doc variable, if not, create it
   Set oApp = GetObject("", "Word.Application")
   oApp.Documents.Open (strPath)
   With oApp
       Set oDoc = oApp.Documents.Item(1)
       If (strExist = "-1") Then
           oDoc.Variables.Add Name:="FormName", Value:=strDocName
           oDoc.Variables.Add Name:="FVersion", Value:=Revision
           'oDoc.Variables.Add Name:="FormName", Value:=strDocName
           'oDoc.Sections(1).Footers(wdHeaderFooterPrimary).Variables.Add
Name:="FormName"
           
oDoc.Sections(1).Footers(wdHeaderFooterPrimary).Range.Fields.Update
           oDoc.Fields.Update