Merge PDF Documents

private void buttonMergePdf_Click(object sender, EventArgs e)
{
    // create an empty document which will become the final document after merge
    PdfDocument resultDocument = new PdfDocument();

    // load the first document to be merged from a file
    string pdfFile1 = Application.StartupPath + @"\DemoFiles\Pdf\WikiHtml.pdf";
    PdfDocument document1 = PdfDocument.FromFile(pdfFile1);

    // load the second document to be merged from a FileStream to exemplify the PDF loading from a stream
    // The stream must remain open until the result document is saved. The stream is closed when the document2 
    // will be closed
    string pdfFile2 = Application.StartupPath + @"\DemoFiles\Pdf\WikiPdf.pdf";
    FileStream pdfStream = new FileStream(pdfFile2, FileMode.Open, FileAccess.Read, FileShare.Read);
    PdfDocument document2 = PdfDocument.FromStream(pdfStream);

    // add the two documents to the result document
    resultDocument.AddDocument(document1);
    resultDocument.AddDocument(document2);

    Cursor = Cursors.WaitCursor;
    string pdfFile = Application.StartupPath + @"\DemoOutput\MergePdf.pdf";
    try
    {
        resultDocument.WriteToFile(pdfFile);
    }
    catch (Exception ex)
    {
        MessageBox.Show(String.Format("Cannot create the PDF document. {0}", ex.Message));
        return;
    }
    finally
    {
        // close the result document
        resultDocument.Close();
        // close the merged documents
        // this will also close the pdfStream from which document 2 was loaded 
        document1.Close();
        document2.Close();

        Cursor = Cursors.Arrow;
    }

    // open the created PDF document
    try
    {
        System.Diagnostics.Process.Start(pdfFile);
    }
    catch (Exception ex)
    {
        MessageBox.Show(String.Format("The PDF document was created but cannot open '{0}'. {1}", pdfFile, ex.Message));
    }
}