Try:
Code:
Sub AddBookmark()
Dim oFld As Field, Rng As Range
For Each oFld In Selection.Fields
If oFld.Type = wdFieldRef Then
Set Rng = oFld.Result
Rng.End = Rng.End + 1
ActiveDocument.Bookmarks.Add Range:=Rng, Name:="test"
Exit For
End If
Next oFld
Set Rng = Nothing
End Sub
Note the 'Exit For'. This serves two purposes, it:
1. avoids needlessly checking any subsequent fields; and
2. prevents any attempt to re-use the bookmark - only one instance of a given bookmark can exist.