This may help:

Sub ScratchMacro()
'A basic Word macro coded by Greg Maxey
Dim oRng As Range
Dim oCDP As DocumentProperty
  'Say you have a bm named "bmDemo" and you want to write text to it ...
  Set oRng = ActiveDocument.Bookmarks("bmDemo").Range
  oRng.Text = "Testing one, two, three ..."
  'Doing that destroys the bookmark so recreate it around the new defined range.
  ActiveDocument.Bookmarks.Add "bmDemo", oRng
  'Say you have a custom document property named "cdpDemo"
  Set oCDP = ActiveDocument.CustomDocumentProperties("cdpDemo")
  'You change its value based:
  oCDP.Value = "Testing one, two, three ..."
  'You have a DocProperty field in the document
  ActiveDocument.Fields.Update
lbl_Exit:
  Exit Sub
End Sub