using GroupDocs.Watermark.Common; using GroupDocs.Watermark.Watermarks; using GroupDocs.Watermark; namespace AddTextWatermarktoPPTXUsingCSharp { internal class Program { static void Main(string[] args) { // Set License to avoid the limitations of Watermark library License lic = new License(); lic.SetLicense(@"GroupDocs.Watermark.lic"); // Specify an absolute or relative path to your PPTX using (Watermarker watermarker = new Watermarker("input.pptx")) { // Specify the desired text and font for the watermark TextWatermark watermark = new TextWatermark("Watermark Text", new Font("Arial", 60, FontStyle.Bold)); // Specify font color and text opacity, rotation and alignments watermark.ForegroundColor = Color.DarkGreen; watermark.Opacity = 0.5; watermark.HorizontalAlignment = HorizontalAlignment.Center; watermark.VerticalAlignment = VerticalAlignment.Center; watermark.RotateAngle = -45; // Apply the watermark watermarker.Add(watermark); // Save the resulting PPTX watermarker.Save("output.pptx"); } } } }