A NotesDocumentCollection is useful for storing a set of documents that you later want to put into a folder or delete; it's a lot faster to make one call than to delete or folder documents one at a time. Unfortunately, there's no simple way to do this such as "Dim dc As NotesDocumentCollection" which is what most people would try. Instead, you have to get it by using one of the search collection APIs with a key that can't be found such as this:
Dim session As New NotesSession Dim dc As NotesDocumentCollection Set dc = session.CurrentDatabase.GetProfileDocCollection("nonexistingform")
or by doing this:
Dim session As New NotesSession Dim db As NotesDatabase Set db = session.CurrentDatabase Dim view As NotesView Set view = db.GetView("($All)") Dim dc As NotesDocumentCollection Set dc = view.GetAllDocumentsByKey("12345") ' non-existent key