เพิ่มลายน้ำในงานนำเสนอ PPTX โดยใช้ C#

using (var presentation = new Presentation())
{
    ISlide slide = presentation.Slides[0];
    IAutoShape watermarkShape = slide.Shapes.AddAutoShape(ShapeType.Triangle, 0, 0, 0, 0);
    ITextFrame watermarkTextFrame = watermarkShape.AddTextFrame("Watermark");

    presentation.Save("watermark.pptx", SaveFormat.Pptx);
}

using (var presentation = new Presentation())
{
    ISlide slide = presentation.Slides[0];
    IAutoShape watermarkShape = slide.Shapes.AddAutoShape(ShapeType.Triangle, 0, 0, 0, 0);

    IPPImage image = presentation.Images.AddImage(File.ReadAllBytes("watermark.png"));

    watermarkShape.FillFormat.FillType = FillType.Picture;
    watermarkShape.FillFormat.PictureFillFormat.Picture.Image = image;
    watermarkShape.FillFormat.PictureFillFormat.PictureFillMode = PictureFillMode.Stretch;

    presentation.Save("watermark2.pptx", SaveFormat.Pptx);
}