UWP WinRT中如何在PDF插入图片并生成无损新PDF？

Hey there! Let's work through your UWP PDF image insertion issue—you need to generate a lossless PDF with image stamps, but the print-to-PDF method is ruining quality, and iText doesn't play nice with UWP. Here are some practical solutions and references to get you sorted:

1. PdfSharpCore: Cross-Platform & UWP-Compatible #

PdfSharpCore is a .NET Core/UWP-friendly port of the popular PdfSharp library, perfect for manipulating PDFs and inserting images without quality loss.

• Key Implementation Steps:
  • Install the PdfSharpCore NuGet package in your UWP project.
  • Load your existing PDF document for modification.
  • Load your target image (stick to lossless formats like PNG/BMP to preserve quality) into an XImage object.
  • Use XGraphics to draw the image onto the desired PDF page at your chosen coordinates.
  • Save the modified PDF to a user-accessible location using UWP's StorageFile APIs.
• Quick Code Snippet:

  using PdfSharpCore.Drawing;
  using PdfSharpCore.Pdf;
  using Windows.Storage;
  using Windows.Storage.Streams;
  
  // Load the input PDF
  PdfDocument pdfDoc = PdfReader.Open("path/to/your/input.pdf", PdfDocumentOpenMode.Modify);
  PdfPage targetPage = pdfDoc.Pages[0]; // Adjust page index as needed
  
  // Load image from storage
  StorageFile imageFile = await StorageFile.GetFileFromPathAsync("path/to/your/image.png");
  using (IRandomAccessStream imageStream = await imageFile.OpenAsync(FileAccessMode.Read))
  {
      XImage stampImage = XImage.FromStream(imageStream.AsStream());
      using (XGraphics gfx = XGraphics.FromPdfPage(targetPage))
      {
          // Draw image at (100,100) with original dimensions
          gfx.DrawImage(stampImage, 100, 100, stampImage.PixelWidth, stampImage.PixelHeight);
      }
  }
  
  // Export the modified PDF
  StorageFile outputFile = await KnownFolders.DocumentsLibrary.CreateFileAsync("stamped_output.pdf", CreationCollisionOption.ReplaceExisting);
  using (IRandomAccessStream outputStream = await outputFile.OpenAsync(FileAccessMode.ReadWrite))
  {
      pdfDoc.Save(outputStream.AsStream());
  }
  

2. Syncfusion Essential PDF for UWP #

Syncfusion offers a robust UWP-specific PDF library with full support for high-quality image insertion. It’s great if you need advanced PDF features beyond just stamping images.

• What to Know:
  • Install the Syncfusion.Pdf.UWP NuGet package.
  • The library lets you add images as stamps or direct page content, with controls to preserve image resolution and quality.
  • Their documentation includes step-by-step guides for UWP, covering everything from loading images to saving the final PDF.

3. Mitigate Print-to-PDF Quality Loss (If You Must Use It) #

If you can’t avoid the system print method, tweak these settings to minimize quality degradation:

• Set PrintTaskOptions.RenderingQuality to PrintRenderingQuality.High (if available in your UWP version).
• Ensure PrintTaskOptions.MediaSize matches the actual PDF page size to avoid unnecessary scaling.
• Note: This will never match the quality of direct PDF manipulation libraries, so it’s a fallback at best.

Pro Tips #

• Always use lossless image formats (PNG, BMP) when inserting stamps—JPEGs will retain their original compression but won’t add extra loss.
• Don’t forget to declare the necessary file access capabilities in your Package.appxmanifest (e.g., DocumentsLibrary, PicturesLibrary) to avoid permission errors when reading/writing files.

内容的提问来源于stack exchange，提问作者Shiv Tyagi