PlaceholderType: Mixed

PowerPoint.Application ppApplication =null;

ppApplication = new PowerPoint.Application();

var Presentations = ppApplication.Presentations;

var Presentation = Presentations.Open(@"Input.pptx", Office.MsoTriState.msoTrue, Office.MsoTriState.msoTrue, Office.MsoTriState.msoTrue);

var Slides = Presentation.Slides;

var slidee = Slides[1];

var shapes = slidee.Shapes;

shapes.AddPlaceholder(Microsoft.Office.Interop.PowerPoint.PpPlaceholderType.ppPlaceholderMixed, 100, 100, 100, 100);

Presentation.Save();