Returns the number of the bookmark that encloses the beginning of the specified selection or range; returns 0 (zero) if there's no corresponding bookmark. The number corresponds to the position of the bookmark in the document
Example
This example displays the number of the bookmark that encloses the beginning of the selection.
MsgBox "Bookmark " & Selection.BookmarkID
This example adds a bookmark named "temp" at the beginning of the document if there's not already a bookmark set for that location.
Set myRange = ActiveDocument.Content
myRange.Collapse Direction:=wdCollapseStart
If myRange.BookmarkID = 0 Then
ActiveDocument.Bookmarks.Add Name:="temp", Range:=myRange
End If