使用 C# 创建 PDF 粘性注释

以下代码片段也适用于 Aspose.PDF.Drawing 库。

添加水印注释

水印注释应用于表示将在页面上以固定大小和位置打印的图形，无论打印页面的尺寸如何。

您可以使用 WatermarkAnnotation 在 PDF 页面上的特定位置添加水印文本。水印的不透明度也可以通过使用不透明度属性进行控制。

请查看以下代码片段以添加 WatermarkAnnotation。

// For complete examples and data files, visit https://github.com/aspose-pdf/Aspose.PDF-for-.NET
private static void AddWatermarkAnnotation()
{
    // The path to the documents directory
    var dataDir = RunExamples.GetDataDir_AsposePdf_Annotations();

    // Open PDF document
    using (var document = new Aspose.Pdf.Document(dataDir + "source.pdf"))
    {
        // Load Page object to add Annotation
        var page = document.Pages[1];

        // Create Watermark Annotation
        var wa = new Aspose.Pdf.Annotations.WatermarkAnnotation(page, new Aspose.Pdf.Rectangle(100, 500, 400, 600));

        // Add annotation into Annotation collection of Page
        page.Annotations.Add(wa);

        // Create TextState for Font settings
        var ts = new Aspose.Pdf.Text.TextState();
        ts.ForegroundColor = Aspose.Pdf.Color.Blue;
        ts.Font = Aspose.Pdf.Text.FontRepository.FindFont("Times New Roman");
        ts.FontSize = 32;

        // Set opacity level of Annotation Text
        wa.Opacity = 0.5;

        // Add Text in Annotation
        wa.SetTextAndState(new string[] { "HELLO", "Line 1", "Line 2" }, ts);

        // Save PDF document
        document.Save(dataDir + "AddWatermarkAnnotation_out.pdf");
    }
}

在 PDF 文档中多次引用单个图像

有时我们需要在 PDF 文档中多次使用相同的图像。添加新实例会增加生成的 PDF 文档。我们在 Aspose.PDF for .NET 17.1.0 中添加了一个新方法 XImageCollection.Add(XImage)。此方法允许将对同一 PDF 对象的引用作为原始图像，从而优化 PDF 文档的大小。

// For complete examples and data files, visit https://github.com/aspose-pdf/Aspose.PDF-for-.NET
private static void AddWatermarkAnnotationWithImage()
{
    // The path to the documents directory
    var dataDir = RunExamples.GetDataDir_AsposePdf_Annotations();

    // Define the rectangle for the image
    var imageRectangle = new Aspose.Pdf.Rectangle(0, 0, 30, 15);

    // Open PDF document
    using (var document = new Aspose.Pdf.Document(dataDir + "input.pdf"))
    {
        // Open the image stream
        using (var imageStream = File.Open(dataDir + "icon.png", FileMode.Open))
        {
            XImage image = null;

            // Iterate through each page in the document
            foreach (Page page in document.Pages)
            {
                // Create a Watermark Annotation
                var annotation = new Aspose.Pdf.Annotations.WatermarkAnnotation(page, page.Rect);
                XForm form = annotation.Appearance["N"];
                form.BBox = page.Rect;

                string name;

                // Add the image to the form resources if it hasn't been added yet
                if (image == null)
                {
                    name = form.Resources.Images.Add(imageStream);
                    image = form.Resources.Images[name];
                }
                else
                {
                    name = form.Resources.Images.Add(image);
                }

                // Add operators to the form contents to place the image
                form.Contents.Add(new Aspose.Pdf.Operators.GSave());
                form.Contents.Add(new Aspose.Pdf.Operators.ConcatenateMatrix(new Aspose.Pdf.Matrix(imageRectangle.Width, 0, 0, imageRectangle.Height, 0, 0)));
                form.Contents.Add(new Aspose.Pdf.Operators.Do(name));
                form.Contents.Add(new Aspose.Pdf.Operators.GRestore());

                // Add the annotation to the page
                page.Annotations.Add(annotation, false);

                // Adjust the image rectangle size for the next iteration
                imageRectangle = new Aspose.Pdf.Rectangle(0, 0, imageRectangle.Width * 1.01, imageRectangle.Height * 1.01);
            }
        }

        // Save PDF document
        document.Save(dataDir + "AddWatermarkAnnotationWithImage_out.pdf");
    }
}