public bool MergePdfFiles(string[] pdfFiles, string outputPath)
    {
        bool result = false;
        int pdfCount = 0;   // total input pdf file count
        int f = 0;  // pointer to current input pdf file
        string fileName = String.Empty; // current input pdf filename
        iTextSharp.text.pdf.PdfReader reader = null;
        int pageCount = 0;  // current input pdf page count
        iTextSharp.text.Document pdfDoc = null; // the output pdf document
        PdfWriter writer = null;
        PdfContentByte cb = null;   // Declare a variable to hold the imported pages
        PdfImportedPage page = null;
        int rotation = 0;   // Declare a font to used for the bookmarks
        iTextSharp.text.Font bookmarkFont = iTextSharp.text.FontFactory.GetFont(iTextSharp.text.FontFactory.HELVETICA, 12, iTextSharp.text.Font.BOLD, iTextSharp.text.Color.BLUE);

        try
        {
            pdfCount = pdfFiles.Length;
            if (pdfCount > 1)
            {
                // Open the 1st pad using PdfReader object
                fileName = pdfFiles[f];
                reader = new iTextSharp.text.pdf.PdfReader(fileName);
                // Get page count
                pageCount = reader.NumberOfPages;
                /*
                Instantiate an new instance of pdf document and set its margins. This will be the output pdf.
                NOTE: bookmarks will be added at the 1st page of very original pdf file using its filename.
                The location of this bookmark will be placed at the upper left hand corner of the document.
                So you'll need to adjust the margin left and margin top values such that the bookmark won't overlay
                on the merged pdf page. The unit used is "points" (72 points = 1 inch), thus in this example, the bookmarks'
                location is at 1/4 inch from left and 1/4 inch from top of the page.
                 */
                pdfDoc = new iTextSharp.text.Document(reader.GetPageSizeWithRotation(1), 18, 18, 18, 18);
                // Instantiate a PdfWriter that listens to the pdf document
                FileStream fs = new FileStream(outputPath, FileMode.Create);
                writer = PdfWriter.GetInstance(pdfDoc, fs);
                // Set metadata and open the document
                pdfDoc.AddTitle("titolo");
                pdfDoc.AddAuthor("autore");
                pdfDoc.AddCreationDate();
                pdfDoc.AddCreator("");  // application name
                pdfDoc.AddSubject("");
                string titles = "";
                pdfDoc.Open();

                // Instantiate a PdfContentByte object
                cb = writer.DirectContent;

                // Now loop thru the input pdfs
                while (f < pdfCount)
                {
                    // save title info or filename for keywords
                    if (reader.Info["Title"] != null && reader.Info["Title"].ToString() != "")
                        titles += "," + reader.Info["Title"].ToString();
                    else
                        titles += ",<" + Path.GetFileName(fileName) + ">";

                    // Declare a page counter variable
                    int i = 0;
                    // Loop thru the current input pdf's pages starting at page 1
                    while (i < pageCount)
                    {
                        i += 1;
                        // Get the input page size
                        pdfDoc.SetPageSize(reader.GetPageSizeWithRotation(i));
                        // Create a new page on the output document
                        pdfDoc.NewPage();
                        // If it is the 1st page, we add bookmarks to the page
                        /*
                        if (i == 1)
                        { 
                            // First create a paragraph using the filename as the heading
                            Paragraph para = new iTextSharp.text.Paragraph(Path.GetFileName(fileName).ToUpper(), bookmarkFont);
                            // Then create a chapter from the above paragraph
                            Chapter chpter = new iTextSharp.text.Chapter(para, f + 1);
                            // Finally add the chapter to the document
                            pdfDoc.Add(chpter);
                        }*/
                        // Now we get the imported page
                        page = writer.GetImportedPage(reader, i);
                        // Read the imported page's rotation
                        rotation = reader.GetPageRotation(i);
                        // Then add the imported page to the PdfContentByte object as a template based on the page's rotation
                        if (rotation == 90)
                            cb.AddTemplate(page, 0, -1.0F, 1.0F, 0, 0, reader.GetPageSizeWithRotation(i).Height);
                        else if (rotation == 270)
                            cb.AddTemplate(page, 0, 1.0F, -1.0F, 0, reader.GetPageSizeWithRotation(i).Width + 60, -30);
                        else
                            cb.AddTemplate(page, 1.0F, 0, 0, 1.0F, 0, 0);
                    }
                    // Increment f and read the next input pdf file
                    f += 1;
                    if (f < pdfCount)
                    {
                        fileName = pdfFiles[f];
                        reader = new iTextSharp.text.pdf.PdfReader(fileName);
                        pageCount = reader.NumberOfPages;
                    }
                }
                // add informations about titles of the original pdf
                pdfDoc.AddKeywords(titles.Substring(1));

                // When all done, we close the documwent so that the pdfwriter object can write it to the output file
                pdfDoc.Close();
                result = true;
            }
        }
        catch(Exception ex)
        {
            throw new Exception(ex.Message);
        }
        return result;
    }