Если у вас Visual Studio 2008, выберите шаблон надстройки PowerPoint.
public partial class ThisAddIn
{//this is the event of the startup of the powerpoint
private void ThisAddIn_Startup(object sender, System.EventArgs e)
{//this is the event that will trigger when you select anything in you presentation
this.Application.WindowSelectionChange += new Microsoft.Office.Interop.PowerPoint.EApplication_WindowSelectionChangeEventHandler(Application_WindowSelectionChange);
}
void Application_WindowSelectionChange(Microsoft.Office.Interop.PowerPoint.Selection Sel)
{
//here you will delete the selected item
Sel.Delete();
}
но я рекомендую вам прочитать больше о надстройке Microsoft, чтобы вы могли достичь желаемого точно