Add-inを使用して選択したSlideにテキストを挿入

PowerPointでRibbonボタンを作成し、このボタンをクリックすると現在のSlideにテキストが挿入されます.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Microsoft.Office.Tools.Ribbon;
using PowerPoint = Microsoft.Office.Interop.PowerPoint;
using System.Windows.Forms;
using Office = Microsoft.Office.Core;

namespace PowerPointAddIn2
{
    public partial class Ribbon1
    {
        private void Ribbon1_Load(object sender, RibbonUIEventArgs e)
        {

        }

        private void button1_Click(object sender, RibbonControlEventArgs e)
        {
            PowerPoint.Application ppApp = Globals.ThisAddIn.Application;
            PowerPoint.SlideRange ppSR = ppApp.ActiveWindow.Selection
                .SlideRange;
            PowerPoint.Shape ppShap = ppSR.Shapes
                .AddLabel(Office.MsoTextOrientation
                .msoTextOrientationHorizontal, 0, 0, 200, 25);
            ppShap.TextEffect.Text = "Hello World!";
        }
    }
}