How to create a zip file for images converted from PDF to PNG

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C#

WinForms

PDF

Bitmap

I want to save files that are converted from a PDF to a PNG in a zip file. So far, I am able to convert a single PDF document into a PNG format, but if the PDF has multiple pages my application only coverts and save them individually (one at a time) in which I have to repeatedly click the Save button before the next page from the PDF is saved, etc.

What I have tried:

I'm using Syncfusion for the document conversion and DotNetZip for zipping the files. Here's my code:

//Loaded PDF file
  PdfLoadedDocument loadedDocument = new PdfLoadedDocument(TxtBox_FileName.Text);

 //ExportAsImage method returns specified page in the PDF document as Bitmap image 
 Bitmap[] images = loadedDocument.ExportAsImage(0, loadedDocument.Pages.Count - 1);

Image imageToConvert = null;
for (int i = 0; i < images.Length; i++)
{
  if(i == 0)
  {
    //Save converted image if PDF is single page
    imageToConvert = images[i];

    SaveFileDialog _saveFile = new SaveFileDialog();
    _saveFile.Title = "Save file";
    _saveFile.Filter = "PNG|*.png";
    _saveFile.FileName = Lbl_FileName.Text;

    if (_saveFile.ShowDialog() == DialogResult.OK)
    {
      imageToConvert.Save(_saveFile.FileName, ImageFormat.Png);

       loadedDocument.Close(true);

       imageToConvert.Dispose();
     }
  }
  else
  {
     //Save converted images if PDF is multi-page
     Image imageToConvert2 = images[i];

     SaveFileDialog _saveFile = new SaveFileDialog();
     _saveFile.Title = "Save file";
     _saveFile.Filter = "PNG|*.png";
     _saveFile.FileName = Lbl_FileName.Text;
     if (_saveFile.ShowDialog() == DialogResult.OK)
     {
        imageToConvert2.Save(_saveFile.FileName, ImageFormat.Png);

         //Create a zip file for all the images 
         string fileName = TxtBox_FileName.Text;
         Thread thread = new Thread(t =>
         {
           using (ZipFile zip = new ZipFile())
           {
              FileInfo fileInfo = new FileInfo(fileName);
              zip.AddFile(fileName);
              DirectoryInfo di = new DirectoryInfo(fileName);
              zip.Save(string.Format("{0}/{1}.zip", di.Parent.FullName, fileInfo.Name));
           }
           })
           { IsBackground = true };
           thread.Start();
          }
          loadedDocument.Close(true);

          imageToConvert2.Dispose();               
     }
 }

Thank you so much for your help!