AutoCAD Activate document problem

I am using AutoCAD full version in my system.I have kept 2 or more AutoCAD drawings minimized. I will select a drawing from vb. I want to insert a drawing to the required AutoCAD drawing which has kept minimized(that is among that 3 drawing I will choose an AutoCAD drawing to which I will insert the selected drawing from vb). I am using lisp code for inserting drawing. From vb I want to select the required AutoCAD file and insert. But every time it is inserting to the first drawing which I have accessed first frm vb6.

I think the title for your thread is a bit confusing. You're not trying to activate a document as much as you are trying to insert a drawing into another AutoCAD drawing that is open but minimized. Is that correct?

For example I have kept 2 autocad windows minimized,in each window kept 2 drawings. On click of the any one drawing the path of the drawing should come to a textbox.

I am using the following code

On Error Resume Next
       Set acadapp = GetObject(, "AutoCAD.Application")
       If Err Then
           Set acadapp = CreateObject("AutoCAD.Application")
           Err.Clear
       End If
Dim strWorkbkName1 As String
strWorkbkName1 = acadapp.ActiveDocument.FullName
Text3.Text = strWorkbkName1

But every time it is taking the first opened window active document ,which I have opened first.it is not showing the second window.Can anyone tell me what is the error in this code.