ITextSharp合并的pdf大小增加

Question

The following code is used to merge multiple pdf file into a single file

public byte[] MergePdfFiles(IEnumerable<byte[]> files)
{
    using (var stream = new MemoryStream())
    {
        var pdfDoc = new iTextSharp.text.Document();
        var pdf = new PdfCopy(pdfDoc, stream);
        pdf.SetMergeFields();

        pdfDoc.Open();

        foreach (var file in files)
        {
            try
            {
                pdf.AddDocument(new PdfReader(file));
            }
            catch (InvalidPdfException ex)
            {
                _loggingServiceClient.Log(LogLevel.Error, ex);
                throw;
            }
        }

        pdfDoc.Close();

        return stream.GetBuffer();
    }
}

The code works fine, BUT the generated file size is almost twice the total size of all merged files. I try to add some compression instructions such as pdf.CompressionLevel = PdfStream.BEST_COMPRESSION; and pdf.SetFullCompression(); with no success.

Note that doing a simple saveAs in acrobat reader from the generated file result in new file with a decent size (the combined size of every merged files).

I also tried other ways to merge file, like using addPage method for example, which end up the same.

Answer 1

Please give this a try:

public byte[] MergePdfFiles(IEnumerable<byte[]> files)
{
    using (var stream = new MemoryStream())
    {
        var pdfDoc = new iTextSharp.text.Document();
        var pdf = new PdfSmartCopy(pdfDoc, stream);
        pdf.SetMergeFields();

        pdfDoc.Open();

        foreach (var file in files)
        {
            try
            {
                pdf.AddDocument(new PdfReader(file));
            }
            catch (InvalidPdfException ex)
            {
                _loggingServiceClient.Log(LogLevel.Error, ex);
                throw;
            }
        }

        pdfDoc.Close();

        return stream.GetBuffer();
    }
}

In case you don't immediately see the difference with your own code: I changed PdfCopy to PdfSmartCopy . If this doesn't help (along with using full compression), there is very little one can do. The main cause is probably the fact that iText can't combine the font subsets of the different files into one new font (which is one of the tricks used by Acrobat to reduce file size).