OK. That takes programming. What is below is the code I use for this. Note,
I only have three address lines in my form. These are Name, Street, and CSZ.
If you have more you'll need to make sure your envelope has fields to match.

It calls up a custom envelope template that I use. That template has
macrobutton fields for manual data entry. See
http://www.addbalance.com/usersguide/fields.htm#MacroButton,
http://www.gmayor.com/Macrobutton.htm and
http://www.mvps.org/word/FAQs/TblsFldsFms/UsingMacroButton.htm for more
about macrobutton fields.

Sub KenyonBillEnvelope()
'
' KenyonEnvelope Macro
' Macro written 7/5/02 by Charles Kyle Kenyon
' "&chr(10)&"New envelope based on Kenyon Envelope form
'   Calls WorkgroupPath Function (below)
'   Calls SelectIt subroutine (below)
'
   Dim sTemplatesPath As String
   Dim sName As String
   Dim sAddress As String
   Dim sCSZ As String
'
   sTemplatesPath = WorkGroupPath & "Letters & Faxes\"
'
'   Get address info from bill
'
   sName = ActiveDocument.FormFields("Name").Result
   sAddress = ActiveDocument.FormFields("Street").Result
   sCSZ = ActiveDocument.FormFields("CSZ").Result
'
'   Create new envelope document and go to place for inserting address
   Documents.Add Template:= _
       sTemplatesPath & "Kenyon Legal Envelope.dot", _
       NewTemplate:=False
   SelectIt (2)
'
'
   Selection.Text = sName
   SelectIt (2)
   Selection.Text = sAddress
   SelectIt (2)
   Selection.Text = sCSZ
   SelectIt (2)
   Selection.Text = ""
   SelectIt (2)
   Selection.Text = ""
   SelectIt (1)
   Selection.Fields.Add Range:=Selection.Range, _
       Type:=wdFieldEmpty, _
       Text:="BARCODE \u """ & sCSZ & """", _
       PreserveFormatting:=False
End Sub

Function WorkGroupPath() As String
'   Written by Charles Kenyon
'   February 28, 2003
'
'   Used by templates menus to set location of templates.
'   Returns workgroup tempates path with "\" at the end.
'
'   This is needed because if the folder is a network drive rather
'   than a folder, it will have the "\" already. If it is a folder,
'   it will not have the backslash. This function gives a string
'   with the backslash in either case.
'
   WorkGroupPath =
Application.Options.DefaultFilePath(wdWorkgroupTemplatesPath)
   If Right(WorkGroupPath, 1) <> "\" Then
       WorkGroupPath = WorkGroupPath & "\"
   End If
End Function

Private Sub SelectIt(iField As Integer)
'   Routine goes to beginning of document and then goes to field
'   iField sets number of field to go to
'   Used in new document menus where fields are present
'   Note - no error handlers so you better have the fields
'
   Dim iNumber As Integer
   Selection.HomeKey Unit:=wdStory
   For iNumber = 1 To iField
       Selection.NextField.Select
   Next iNumber
End Sub

See http://word.mvps.org/FAQs/MacrosVBA/CreateAMacro.htm or
http://gmayor.com/installing_macro.htm for information on how to put these
in your templates. You can download some sample envelope templates from
http://gmayor.com/Zips/Envelope.zip.