Play with this to get you started:

Dim i As Long

With ActiveDocument
   For i = Paragraphs.Count To 1 Step -1
       If .Paragraphs(i).Style = "Web ID" Then
           .Bookmarks.Add "ID_" & Left(.Paragraphs(i).Range.Text, _
               Len(.Paragraphs(i).Range.Text) - 1), .Paragraphs(i + 1).Range
           .Paragraphs(i).Range.Delete
       End If
   Next
End With

A few words regarding bookmarks:
The first character cannot be a number (This is why I include the "ID_"
string).
The length limit is 40 characters.
There cannot be any spaces in the bookmark names.
Names must be unique, if they are not, the new one will be created, but the
old one with the same name will be automatically removed.

So, depending on the nature of the content of your ID string of text, you
may need to tweak the code...