使用 iTextSharp 压缩 Pdf

Question

我在网上找到了许多示例，其中之一：

var oldFile = @"C:\Users\XXX\Downloads\3921B2014901_2014_7346.pdf";
var newFile = @"C:\Users\XXX\Downloads\new\3921B2014901_2014_7346.pdf";

RandomAccessFileOrArray raf = new RandomAccessFileOrArray(oldFile);
PdfReader reader = new PdfReader(raf, null);
using (FileStream fs = new FileStream(newFile, FileMode.Create))
{
    PdfStamper stamper = new PdfStamper(reader, fs, PdfWriter.VERSION_1_5);
    PdfWriter writer = stamper.Writer;
    writer.SetPdfVersion(PdfWriter.PDF_VERSION_1_5);
    writer.CompressionLevel = PdfStream.BEST_COMPRESSION;

    for (int i = 1; i <= reader.NumberOfPages; i++)
    {
        reader.SetPageContent(i, reader.GetPageContent(i), PdfStream.BEST_COMPRESSION, true);
    }
    stamper.SetFullCompression();
    stamper.Close();
}
reader.Close();
raf.Close();

原始文件为 2.75Mb，生成的新文件为 2.77Mb。为什么？

我尝试了在线转换器，它们将同一文件减少到 500Kb。我怎样才能达到同样的效果？

Answer 1

protected void btnCompressPdf_click(object sender, EventArgs e)
{  
    string[] filename= Directory.GetFiles(input.Text, ".jpg");
    string outputPath = MyDirectory;
    if (!System.IO.Directory.Exists(MyDirectory))
        System.IO.Directory.CreateDirectory(MyDirectory);

    foreach (string filename in files)
    {
        ImageCollection images = new ImageCollection();
        images.Add(filename);
        String pdfName = Path.GetFileNameWithoutExtension(file);
        for (int pageNumber = 0; pageNumber < images.Count; pageNumber++)
        {
            images[pageNumber].Save(MyDirectory + "\\" + pageNumber.ToString() + ".jpg");
        }

        string[] files1 = System.IO.Directory.GetFiles(MyDirectory, ".jpg");

        iTextSharp.text.Document myDocument = new iTextSharp.text.Document(iTextSharp.text.PageSize.A4, 0, 0, 0, 0);
        //PdfWriter.GetInstance(myDocument, new System.IO.FileStream(uxOutput.Text + "\\" + pdfName + ".pdf", System.IO.FileMode.Create));
        PdfWriter writer = PdfWriter.GetInstance(myDocument, new System.IO.FileStream(Output.Text + "\\" + pdfName + ".pdf", System.IO.FileMode.Create));
        writer.SetPdfVersion(PdfWriter.PDF_VERSION_1_5);
        writer.CompressionLevel = PdfStream.BEST_COMPRESSION;
        writer.SetFullCompression();
        for (int i = 0; i <= files1.Length - 1; i++)
        {
            if (myDocument != null)
            {
                myDocument.Open();
                AddImageToPDF(myDocument, MyDirectory + "\\" + (i).ToString() + ".jpg");
            }
        }
        myDocument.Close();
        myDocument = null;
        System.IO.File.Delete(MyDirectory + "\\" + ".jpg");
    }
}