Proteja XLSX hojas con .NET C#

    //  Cargar presentación de PPTX
    var loadOptions = new PresentationLoadOptions();
    using (Watermarker watermarker = new Watermarker("source.pptx", loadOptions))
    {
        //  Configurar las propiedades de las marcas de agua
        TextWatermark watermark = new TextWatermark("Protected image", new Font("Arial", 8));
        watermark.HorizontalAlignment = HorizontalAlignment.Center;
        watermark.VerticalAlignment = VerticalAlignment.Center;
        watermark.RotateAngle = 45;
        watermark.SizingType = SizingType.ScaleToParentDimensions;
        watermark.ScaleFactor = 1;

        //  Fondo de diapositivas con marca de agua
        PresentationContent content = watermarker.GetContent<PresentationContent>();
        foreach (PresentationSlide slide in content.Slides)
        {
            if (slide.ImageFillFormat.BackgroundImage != null)
            {
                slide.ImageFillFormat.BackgroundImage.Add(watermark);
            }
        }

        //  Guardar presentación procesada
        watermarker.save("result.pptx");
    }