Make WPF window draggable, no matter what element is clicked

Sure, apply the following MouseDown event of your Window

private void Window_MouseDown(object sender, MouseButtonEventArgs e)
{
    if (e.ChangedButton == MouseButton.Left)
        this.DragMove();
}

This will allow users to drag the Window when they click/drag on any control, EXCEPT for controls which eat the MouseDown event (e.Handled = true)

You can use PreviewMouseDown instead of MouseDown, but the drag event eats the Click event, so your window stops responding to left-mouse click events. If you REALLY wanted to be able to click and drag the form from any control, you could probably use PreviewMouseDown, start a timer to begin the drag operation, and cancel the operation if the MouseUp event fires within X milliseconds.