Combinar formatos PPSX en C#

var ps1 = new Presentation("presen1.ppsx");
    var ps2 = new Presentation("presen2.pptx");
    
    //merged Presentation 
    var mp = new Presentation("template.pptx");
    while (mp.Slides.Count > 0){
        mp.Slides.RemoveAt(0);
    }
    // master slide
    var ms = mp.Masters[0];
    
    // The first PPSX presentation is added with its own styles.
    foreach (var slide in ps1.Slides){
        mp.Slides.AddClone(slide);
    }
    
    // The second PPTX presentation is added with template presentation styles using.
    foreach (var slide in ps2.Slides){
        mp.Slides.AddClone(slide, ms, true);
    }
    
    // It is possible to save the merged presentation to any supported format.
    mp.Save("mp.pptx", SaveFormat.Pptx);
    mp.Save("mp.pptx", SaveFormat.Pdf);