The code I use is as below:

Function Item_Open()
MyValue = item.UserProperties("request")
Set myInspector = Item.GetInspector
Set myPages = myInspector.ModifiedFormPages
If MyValue "" Then
If MyValue = "1" Then
myInspector.ShowFormPage("1")
myInspector.HideFormPage("2")
myInspector.HideFormPage("3")
myInspector.HideFormPage("4")
ElseIf MyValue = "2" Then
myInspector.ShowFormPage("2")
myInspector.HideFormPage("1")
myInspector.HideFormPage("3")
myInspector.HideFormPage("4")
ElseIf MyValue = "3" Then
myInspector.ShowFormPage("3")
myInspector.HideFormPage("1")
myInspector.HideFormPage("2")
myInspector.HideFormPage("4")
ElseIf MyValue = "4" Then
myInspector.ShowFormPage("4")
myInspector.HideFormPage("1")
myInspector.HideFormPage("2")
myInspector.HideFormPage("3")
Else
myInspector.ShowFormPage("1")
myInspector.ShowFormPage("2")
myInspector.ShowFormPage("3")
myInspector.ShowFormPage("4")
End If
End If
End Function

Now, the recipient is still seeing all 4 pages. Also, on Reply by the
recipient, the form is lost. The form is still attached only if the
recipient forwards it back to the original sender or forwards it to
another person.

I have also tried the Sub Item_CustomPropertyChange(ByVal Name) and
added the above code, but the same is working only for the original
sender.