Merging word documents keeping format in VB NET

I am writing a program that is supposed to merge several word documents into one keeping the formatting of each document. After some research on the web wrote a version that is supposed to work, which is the following:

Public Sub processmodulestest(ByVal id As Integer)
    Dim oMissing = System.Reflection.Missing.Value
    Dim oFalse = False
    Dim oTrue = True
    Dim fileDirectory = "C:\<file-path>\MOD-TEST\"

    Dim wrdApp As New Word.Application
    Dim destDoc As Word.Document 'destination doc
    Dim docfile As Word.Document 'tmp doc to paste
    destDoc = wrdApp.Documents.Add

    'docNew.PageSetup.TopMargin = wrdApp.InchesToPoints(1.0F)
    'docNew.PageSetup.BottomMargin = wrdApp.InchesToPoints(0.0F)
    Dim wordFiles() As String = Directory.GetFiles(fileDirectory, "*.doc")

    wrdApp.Options.Pagination = False
    wrdApp.ActiveWindow.View.ShowAll = True

    For Each el As String In wordFiles
        docfile = wrdApp.Documents.Open(el, False, False)
        wrdApp.Selection.WholeStory()
        wrdApp.Selection.Copy()
        wrdApp.ActiveWindow.Close(Word.WdSaveOptions.wdDoNotSaveChanges)
        destDoc.Activate()
        wrdApp.Selection.PasteAndFormat(Word.WdRecoveryType.wdFormatOriginalFormatting)
        wrdApp.Selection.InsertBreak(Word.WdBreakType.wdPageBreak)
    Next

    wrdApp.Visible = True
End Sub

I get the following Error:

An unhandled exception of type'System.Runtime.InteropServices.COMException' 
HRESULT: 0x80010108 (RPC_E_DISCONNECTED)) The object invoked has disconnected from its clients.

referring to the following line:

destDoc.Activate()

I read that this should be because the code uses an unqualified method on an Office instance that has been ended, but i can't understand how to fix it

I'm not sure how to do it in VB.NET, but the VBA code below will merge all Word documents into one single consolidated Word document.

Appending multiple Word docs into a single Word doc

Sub Foo()
Dim i As Long
Dim MyName As String, MyPath As String
Application.ScreenUpdating = False
Documents.Add

MyPath = "C:\Documents and Settings\Excel\Desktop\Word Files\" ' <= change this as necessary

MyName = Dir$(MyPath & "*.doc") ' not *.* if you just want doc files

Do While MyName <> ""
If InStr(MyName, "~") = 0 Then
Selection.InsertFile _
FileName:="""" & MyPath & MyName & """", _
ConfirmConversions:=False, Link:=False, _
Attachment:=False
Selection.InsertBreak Type:=wdPageBreak
End If

MyName = Dir ' gets the next doc file in the directory
Loop

End Sub