AutoCAD .NET :: How To Switch Between Multiple Open Documents

I am a total  beginner at this vb.net thing.  I have a vba routine that I have used for years to execute a lisp routine on an open document, then switch to the next already open document, and continue until the routine has been performed on each already open documents.  For the life of me, I cannot figure out how in vb.net to get a document collection and make each document the active document so that I can execute the lisp routine.

VBA

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Option Explicit
    Dim objAcadApp As AcadApplication       'Acad application object
    Dim objAcadDocs As AcadDocuments        'Acad documents collection
    Dim objAcadDoc As AcadDocument          'Acad document object
    Dim i As Integer

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