Spliting PDF and get thumbnail while adding it to a ListView

Question

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.

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

CODE

public void SplitPDF2(string input)
{
    try
    {
        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);
                    image.Dispose();
                }
                //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);
                    doc.Open();
                    PdfContentByte pdfContentByte = pdfWriter.DirectContent;
                    PdfImportedPage importedpage = pdfWriter.GetImportedPage(reader, i);
                    iTextSharp.text.Rectangle mediabox = reader.GetPageSize(i);

                    doc.SetPageSize(mediabox);
                    doc.NewPage();
                    pdfContentByte.AddTemplate(importedpage, 0, 0);

                    doc.Close();
                    doc.Dispose();
                    pdfWriter.Dispose();
                }
                //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

                lista2.Items.Add(_item1);
                j++;
            }
        }
        reader.Dispose();
    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.ToString(), "Erro", MessageBoxButtons.OK);
    }
}

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?

Non-minor:

• 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.