I'm doing a application to work with PDF and TIFF files. To divide them, the user opens the file or folder (if it is a folder, it gets all the files inside) and the app splits the file, getting a tiny image (thumbnail) in JPG format. Then it creates a ListViewItem adding the thumbnail, the name and the size of the file.

But it takes too long (1:40min) with a PDF with 68 pages, so if a larger PDF is opened, it will take too long.

the time for 68 pages

So I wish someone could say where can I improve my code so it doesn't take that long.


public void SplitPDF2(string input)
        iTextSharp.text.pdf.PdfReader reader = new iTextSharp.text.pdf.PdfReader(input);
        iTextSharp.text.pdf.PdfReader.unethicalreading = true;
        string name = Path.GetFileNameWithoutExtension(input);
        for (int i = 1; i <= reader.NumberOfPages; i++)
            using (MemoryStream ms = new MemoryStream())
                //get thumbnail from 1st page-----------------------------------------------------                       
                using (var document = PdfiumViewer.PdfDocument.Load(input))
                    var image = document.Render(i - 1, 60, 84, 300, 300, true);                            
                    image.Save(ms, ImageFormat.Jpeg);
                    thumbnails.Images.Add(j.ToString(), image);
                //split pdf-----------------------------------------------------------------------
                string p = AppDomain.CurrentDomain.BaseDirectory + "temporario\\" + name + " - Pagina " + i + ".PDF";
                using (Stream outputStream = new FileStream(p, FileMode.Create))
                    Document doc = new Document();
                    PdfWriter pdfWriter = PdfWriter.GetInstance(doc, outputStream);
                    PdfContentByte pdfContentByte = pdfWriter.DirectContent;
                    PdfImportedPage importedpage = pdfWriter.GetImportedPage(reader, i);
                    iTextSharp.text.Rectangle mediabox = reader.GetPageSize(i);

                    pdfContentByte.AddTemplate(importedpage, 0, 0);

                //in the end it will add the thumbnail, the name and the size of the file to the ListView 
                FileInfo f = new FileInfo(p);
                ListViewItem _item1 = new ListViewItem();
                _item1.ImageKey = j.ToString(); //image
                _item1.SubItems.Add(name + " - Pagina " + i + ".PDF"); //name
                _item1.SubItems.Add(f.Length.ToString()); //size

    catch (Exception ex)
        MessageBox.Show(ex.ToString(), "Erro", MessageBoxButtons.OK);
  • 3
    \$\begingroup\$ Why are you saving the images on the disk and not working with them in memory? You seem to mix a couple of principles there. using and Dispose at the same time, no using in other cases... quite a mess. \$\endgroup\$
    – t3chb0t
    Apr 29, 2019 at 8:40
  • \$\begingroup\$ How should I do it using the memory? Using a MemoryStream? @t3chb0t \$\endgroup\$ Apr 29, 2019 at 8:43
  • \$\begingroup\$ @t3chb0t Could you help me organizing and "unmessing" my code? \$\endgroup\$ Apr 29, 2019 at 10:19
  • \$\begingroup\$ Welcome! You might want to take a look at profiling: docs.microsoft.com/en-us/visualstudio/profiling/?view=vs-2019 \$\endgroup\$
    – user50167
    Nov 12, 2019 at 16:43

1 Answer 1


This code leaves a bunch of open questions, minor ones:
- SplitPDF2(string input) what has been/happened to SplitPDF() or SplitPDF1()?
- what is lista2?


  • Document/comment your source code. In the code.
  • Preparing thumbnails and splitting a PDF into separate-file-per-page do neither sound nor look related:
    Do not put/implement both in a single procedure
  • I can't seem to see a purpose in saving each thumbnail rendered into a MemoryStream ms that doesn't get used otherwise.
  • You instantiate one and only one iTextSharp.text.pdf.PdfReader(input) for each input:
    Do the same for PdfiumViewer.PdfDocument
  • it will add the thumbnail I don't see that.

Overall, I'm left mistrusting writing file-per-page PDF to be a useful step in accomplishing the larger task at hand.
wish someone could say where [to improve the] code so it doesn't take that long my crystal ball is dull, but profiling/timeit() might help.

  • \$\begingroup\$ Thank you for your answer and I’m no longer working with that... since I am portuguese, some variables can be strange to you, such as “lista2”, my appologies. If I remember it well, the other SplitPDF() functions were with another libraries. I’m sure that who uses your answer to resolve their problems, it will help them. \$\endgroup\$ Nov 13, 2019 at 16:08

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