Managing custom task panes across multiple documents in shared add in for office 2007 using .NET

I see a lot of articles on this topic but all are related to VSTO. But I required this for shared addin. I followed MSDN to create custom task pane using shared addin. It works fine but when multiple documents are opened then it appears only for the first document. I have implemented to show document wise custom task pane.

using MSword = Microsoft.Office.Interop.Word;
public class Connect : Object, Extensibility.IDTExtensibility2,  ICustomTaskPaneConsumer 
{
public Connect()
{
}
public void OnConnection(object application, Extensibility.ext_ConnectMode connectMode, object addInInst, ref System.Array custom)
{
applicationObject = (MSword.Application)application;
addInInstance = addInInst;

}
public void OnStartupComplete(ref System.Array custom)
{
applicationObject.DocumentOpen += new Microsoft.Office.Interop.Word.ApplicationEvents4_DocumentOpenEventHandler(applicationObject_DocumentOpen);
applicationObject.WindowActivate += new Microsoft.Office.Interop.Word.ApplicationEvents4_WindowActivateEventHandler(applicationObject_WindowActivate); 
}
void applicationObject_DocumentOpen(Microsoft.Office.Interop.Word.Document Doc)
{   
AddCustomTaskPane();             
}
void applicationObject_WindowActivate(Microsoft.Office.Interop.Word.Document Doc, Microsoft.Office.Interop.Word.Window Wn)
{
}
public void OnBeginShutdown(ref System.Array custom)
{
}
public void OnDisconnection(Extensibility.ext_DisconnectMode disconnectMode, ref System.Array custom)
{
}
public void OnAddInsUpdate(ref System.Array custom)
{
}
private MSword.Application applicationObject;
private object addInInstance;        

#region ICustomTaskPaneConsumer Members
ICTPFactory ctpFactory;
object missing = Type.Missing;


public void CTPFactoryAvailable(ICTPFactory CTPFactoryInst)
{
ctpFactory = CTPFactoryInst;
AddCustomTaskPane(); 
}
public void AddCustomTaskPane()
{
CustomTaskPane CTP = ctpFactory.CreateCTP("MyNameSpace.MyUserControl", "My Task Pane", missing);
MyUserControl sampleAX = (MyUserControl)CTP.ContentControl;               
CTP.Visible = true;        
}


#endregion
}