Tab Navigation not working When running c# Winform from WPF

Question

I'm creating a Visual Studio project as WPF application. but presently I am creating only Windows forms inside that project. I have plans to convert them to WPF in future, that's why I created the project as WPF application.

I set one of my windows forms as Startup form in App.xaml. The forms are loading and everything works fine except the tab navigation. The first control gets focused on the startup, but when I press Tab key the focus is not moving to the next control.

This is my App.xaml.cs file

namespace WpfTest 
{ 
   /// <summary> 
   /// Interaction logic for App.xaml 
   /// </summary> 
   public partial class App : Application 
   { 
      private void Application_Startup(object sender, StartupEventArgs e)
      {         
        frmStudent frm = new frmStudent(); 
        frm.Show(); 
      } 
    } 
 }

This is my App.xaml file

<Application x:Class="WpfTest.App"          
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"          
             xmlns:local="clr-namespace:WpfTest" Startup="Application_Startup"> 
   <Application.Resources>  
   </Application.Resources> 
</Application>

I have created a sample project in Visual Studio 2015 to illustrate the problem and attached  You can download it from here. I am a newbie in WPF.