Merge pdf files using itextshatp

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C#

Trying to do a simple Merge pdf files using itextshatp, however no Result/Merged file is created and no errors thrown. Am I missing anything?

What I have tried:

 private void CreateMergedPdf(object sender, DoWorkEventArgs e)
 {
using (FileStream StreamMulti=new FileStream(MergeOutputPdfName,FileMode.Create))
     {
         Document DocumentMulti = new Document();
         PdfCopy WriterMulti = new PdfCopy(DocumentMulti,StreamMulti);
         DocumentMulti.Open();

         try
         {
             foreach (string fileItem in ListBox.Items)
             {
                 PdfReader ReaderMulti = PdfReader(fileItem);
                 WriterMulti.AddDocument(ReaderMulti);
                 ReaderMulti.Close();
             }
         }
         catch (Exception Ex)
         {
             MessageBox.Show(Ex.Message," Merge Error !",MessageBoxButtons.OK,MessageBoxIcon.Error);
         }
         WriterMulti.Close();
         DocumentMulti.Close();
     }
 }