How to stop the rehreased powerpoint or set focus out of the powerpoint in C# ?

I am playing powerpoint in my window.

As you can see in this image window has two section, one is on the top that has tool bar where i have option like text, start button and etc. Now if my powerpoint is rehearsed in that case when i click on the text powerpoint should not be in active state ( it should be in deactivate state). but when i click on the start button it should be activated (rehearsed powerpoint should play). By default when this window launch focus is on start button.

What is happening here : When i click on text powerpoint is activated. that i dont want. how can i achive that ?

This is code that i am using on MouseLeftButtonDown event on the text :

 private void txtPlayingAudio_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
        {
        PrerecordTooltip.Text = "Click to pause audio";
        BrushConverter bc = new BrushConverter();
        txtPlayingAudio.Foreground = (System.Windows.Media.Brush)bc.ConvertFrom("#007dc7");
        btnStart.Focus();

}}

Thanks