# Add Presentation Watermarks > Apply text and image watermarks to slides, then remove only the shapes identified by your application. Source: https://docs.aspose.com/slides/net/examples/presentations/watermarks/ Updated: 2026-10-31 Apply text and image watermarks to slides, then remove only the shapes identified by your application. ## Download and run Download [the complete project](example.zip) and open **Example.sln** in a compatible IDE. Automatic NuGet restore should run when it opens. The project accepts supported installed release SDKs instead of requiring one exact patch. [Setup and supported environments](/slides/net/examples/getting-started/) explains native libraries, fonts and the SDK/runtime distinction. ```text dotnet run --project Example.csproj -- --mode evaluation ``` Evaluation mode needs no license and retains the SDK watermark/text limits. For full licensed checks, set ASPOSE_LICENSE_PATH to your authorized license and use --mode licensed. Fonts and synthetic fixtures needed by this recipe are included or acquired as documented. The supplied bootstrap prepares a separate output workspace and prints its absolute path. The complete download includes that bootstrap, solution and editor profiles; the C# block below is Program.cs from the same archive. ## Input and prerequisites The code creates its own synthetic input. Use a compatible stable SDK with the included Aspose.Slides.NET6.CrossPlatform 26.10.0 project; .NET 10 LTS is recommended. Evaluation mode performs the recipe without a license and retains the SDK watermark and text limits. Licensed mode additionally checks unrestricted content using your authorized license. [Download the complete project](example.zip), including the solution, source, configuration and bundled fonts. No license is distributed. ## Example This example chooses slide-level watermarks so each target slide receives the marker independently of its layout. The original PNG is generated by the code. AlternativeText stores an application-specific marker; removal matches that marker rather than deleting every shape containing the word DRAFT. ```csharp using System.Threading.Tasks; using System; using System.Collections.Generic; using System.Drawing; using System.IO; using System.Linq; using System.Security.Cryptography; using System.Text.Json; using Aspose.Slides; using Aspose.Slides.Export; internal static class Program { private static ExampleContext Context = null!; private static Task Main(string[] args) => ExampleBootstrap.RunAsync(args, async context => { Context = context; context.BeginAction("presentations/watermarks/block-001"); RunExample(); await Task.CompletedTask; context.Pass("presentations/watermarks/block-001", "recipe semantic assertions", "source inputs preserved", "documented output generated"); }); private const string WatermarkTag = "example-watermark:"; private static void MarkText(Presentation presentation) { foreach (var slide in presentation.Slides) { var shape = slide.Shapes.AddAutoShape(ShapeType.Rectangle, 100, 150, 440, 70); shape.AlternativeText = WatermarkTag + "text"; shape.FillFormat.FillType = FillType.NoFill; shape.LineFormat.FillFormat.FillType = FillType.NoFill; shape.Rotation = -25; shape.TextFrame.Text = "DRAFT"; var format = shape.TextFrame.Paragraphs[0].Portions[0].PortionFormat; format.FontHeight = 52; format.FillFormat.FillType = FillType.Solid; format.FillFormat.SolidFillColor.Color = Color.FromArgb(90, Color.Gray); } } private static void MarkImage(Presentation presentation) { var image = presentation.Images.AddImage(File.ReadAllBytes("watermark.png")); foreach (var slide in presentation.Slides) { var frame = slide.Shapes.AddPictureFrame(ShapeType.Rectangle, 460, 270, 150, 50, image); frame.AlternativeText = WatermarkTag + "image"; } } private static void RemoveOurWatermarks(Presentation presentation) { foreach (var slide in presentation.Slides) for (int i = slide.Shapes.Count - 1; i >= 0; i--) if (slide.Shapes[i].AlternativeText.StartsWith(WatermarkTag, StringComparison.Ordinal)) slide.Shapes.RemoveAt(i); } private static void RunExample() { using (var logo = new Presentation()) { logo.SlideSize.SetSize(150, 50, SlideSizeScaleType.DoNotScale); var slide = logo.Slides[0]; slide.Background.Type = BackgroundType.OwnBackground; slide.Background.FillFormat.FillType = FillType.Solid; slide.Background.FillFormat.SolidFillColor.Color = Color.LightGoldenrodYellow; var circle = slide.Shapes.AddAutoShape(ShapeType.Ellipse, 8, 8, 34, 34); circle.FillFormat.FillType = FillType.Solid; circle.FillFormat.SolidFillColor.Color = Color.DarkOrange; var bar = slide.Shapes.AddAutoShape(ShapeType.Rectangle, 52, 17, 84, 16); bar.FillFormat.FillType = FillType.Solid; bar.FillFormat.SolidFillColor.Color = Color.DarkSlateBlue; using var rendered = slide.GetImage(new Size(150, 50)); rendered.Save("watermark.png", Aspose.Slides.ImageFormat.Png); } using (var created = new Presentation()) { created.SlideSize.SetSize(640, 360, SlideSizeScaleType.DoNotScale); Label(created.Slides[0], "Original DRAFT content"); // Must survive removal. var second = created.Slides.AddEmptySlide(created.LayoutSlides.GetByType(SlideLayoutType.TitleOnly)); Label(second, "Second layout"); created.Save("input.pptx", SaveFormat.Pptx); } string inputHash = Hash("input.pptx"); using (var text = new Presentation("input.pptx")) { MarkText(text); text.Save("text-watermark.pptx", SaveFormat.Pptx); using var preview = text.Slides[0].GetImage(new Size(640, 360)); preview.Save("preview-text.png", Aspose.Slides.ImageFormat.Png); } using (var image = new Presentation("text-watermark.pptx")) { MarkImage(image); image.Save("image-watermark.pptx", SaveFormat.Pptx); for (int i = 0; i < image.Slides.Count; i++) { Require(image.Slides[i].Shapes.Count(s => s.AlternativeText.StartsWith(WatermarkTag, StringComparison.Ordinal)) == 2, "A watermark is missing."); using var preview = image.Slides[i].GetImage(new Size(640, 360)); preview.Save($"preview-image-{i + 1}.png", Aspose.Slides.ImageFormat.Png); } RemoveOurWatermarks(image); image.Save("removed.pptx", SaveFormat.Pptx); } using (var original = new Presentation("input.pptx")) using (var removed = new Presentation("removed.pptx")) { Require(removed.Slides.Count == original.Slides.Count, "Slide count changed."); Require(removed.Slides.All(s => !s.Shapes.Any(x => x.AlternativeText.StartsWith(WatermarkTag, StringComparison.Ordinal))), "A tagged application watermark remains."); for (int i = 0; i < original.Slides.Count; i++) { Require(ApplicationShapes(removed.Slides[i]).Count() == ApplicationShapes(original.Slides[i]).Count(), "Original shape count changed."); Require(Text(removed.Slides[i]) == Text(original.Slides[i]), "Original text changed."); Require(ApplicationShapes(removed.Slides[i]).Select(s => s.Name).SequenceEqual(ApplicationShapes(original.Slides[i]).Select(s => s.Name)), "Original shape identities changed."); } } Require(Hash("input.pptx") == inputHash, "The source was overwritten."); Report(new { slides = 2, text_and_image_applied = true, multiple_layouts_rendered = true, originals_retained = true, tagged_removal_only = true, original_unchanged = true }); } private static void Require(bool condition, string message) { if (!condition) throw new InvalidOperationException(message); } private static IAutoShape Label(ISlide slide, string text) { var shape = slide.Shapes.AddAutoShape(ShapeType.Rectangle, 50, 80, 540, 100); shape.Name = "content-" + text; shape.TextFrame.Text = text; shape.TextFrame.Paragraphs[0].Portions[0].PortionFormat.FontHeight = 28; return shape; } private static string Text(ISlide slide) => string.Join("|", slide.Shapes.OfType().Where(s => s.Name.StartsWith("content-", StringComparison.Ordinal)).Select(s => s.TextFrame.Text)); // Evaluation adds SDK-owned watermark shapes during serialization; compare our content without removing those SDK marks. private static IEnumerable ApplicationShapes(ISlide slide) => slide.Shapes.Where(s => Context.IsLicensed || s.Name.StartsWith("content-", StringComparison.Ordinal)); private static string Hash(string file) => Convert.ToHexString(SHA256.HashData(File.ReadAllBytes(file))); private static void Report(object checks) { string json = JsonSerializer.Serialize(new { checks }, new JsonSerializerOptions { WriteIndented = true }); File.WriteAllText("result.json", json); Console.WriteLine(json); } } ``` ## Run and check the result Extract the project into an empty working directory, restore its locked packages, then run it: ```text dotnet restore Example.csproj --locked-mode dotnet run --project Example.csproj --configuration Release --no-restore ``` The example writes "watermark.png", "input.pptx", "text-watermark.pptx", "image-watermark.pptx", "removed.pptx", "preview-text.png", "preview-image-1.png", "preview-image-2.png" and "result.json". It reopens the generated presentation files and checks the expected data. A failed check raises an exception; successful checks are recorded in "result.json". ## Output previews ![preview text](preview-text.png) ![preview image 1](preview-image-1.png) ![preview image 2](preview-image-2.png) ## Practical limits A watermark is a visual label and can be edited or removed; it does not encrypt or restrict access to the presentation. Reserve an unambiguous marker in your own application. A master-level watermark is another option, but its visibility depends on slide and layout settings. The small PNG is rendered from original shapes by the example itself. See the [detailed guide](/slides/net/watermark/) and [individual slide examples](/slides/net/examples/elements/slide/).