powerpoint automation and c#

Namespaces needed

using PowerPoint = Microsoft.Office.Interop.PowerPoint;
using Microsoft.Office.Core;

namespace WindowsFormsApplication8
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {

================================================================

            PowerPoint._Application ppApp;// a powerpoint applin 
            PowerPoint.Presentation ppMP;///a powerpoint presentation

            ppApp = new PowerPoint.Application();////opening a powerpoint applin 
            Microsoft.Office.Core.MsoTriState ofalse = Microsoft.Office.Core.MsoTriState.msoFalse;
            Microsoft.Office.Core.MsoTriState otrue = Microsoft.Office.Core.MsoTriState.msoTrue;
            ppApp.Visible = otrue;
            ppApp.Activate();

================================================================

//saving it
            ppMP = ppApp.Presentations.Open(@"C:\Users\snair02\Desktop\SRJ DOCS\raj.pptx",ofalse,ofalse,otrue);

             PowerPoint.Slides oSlides = ppMP.Slides;
            foreach (PowerPoint.Slide oSlide in oSlides)
            {
                foreach (PowerPoint.Shape shape in oSlide.Shapes)
                {
                    shape.TextFrame.TextRange.Text = shape.TextFrame.TextRange.Text.Replace("*", "Hi I am Sreeraj");
                }
            }
        }
    }
}