using PowerPoint = Microsoft.Office.Interop.PowerPoint;
using Graph = Microsoft.Office.Interop.Graph;
using Microsoft.Office.Core;
String sourcePPTPath= @"e:\test.pptx";
PowerPoint.Application pptApp = new PowerPoint.Application();
PowerPoint.Presentations pptDocSet = pptApp.Presentations;
PowerPoint._Presentation pptDoc = pptDocSet.Open(sourcePPTPath, MsoTriState.msoFalse, MsoTriState.msoFalse, MsoTriState.msoFalse);