how to merge pdf file [iTextSharp]

Make 3 instance

  MemoryStream stream  =   new  MemoryStream();
            Document doc  =   new  Document();
            PdfCopy writer  =   new  PdfCopy(doc, stream);
            doc.Open();

Read what page you need.
add these page to writer.
index is start at 1

string  path2  = " . " ;   
PdfReader pf  =   new  PdfReader(path2);

                page  =   writer.GetImportedPage(pf,  1 );
                writer.AddPage(page);

close

   pf.Close();   
doc.Close();
             return  stream;