    protected void mergePdfButton_Click(object sender, EventArgs e)
    {
        // Create the merge result PDF document
        Document mergeResultPdfDocument = new Document();

        // Automatically close the merged documents when the document resulted after merge is closed
        mergeResultPdfDocument.AutoCloseAppendedDocs = true;

        // Set license key received after purchase to use the converter in licensed mode
        // Leave it not set to use the converter in demo mode
        mergeResultPdfDocument.LicenseKey = "4W9+bn19bn5ue2B+bn1/YH98YHd3d3c=";

        try
        {
            // The documents to merge must remain opened until the PDF document resulted after merge is saved
            // The merged documents can be automatically closed when the document resulted after merge is closed
            // if the AutoCloseAppendedDocs property of the PDF document resulted after merge is set on true like
            // in this demo applcation

            // Load the first PDF document to merge
            string firstPdfFilePath = Server.MapPath("~/DemoAppFiles/Input/PDF_Files/Merge_Before_Conversion.pdf");
            Document firstPdfDocumentToMerge = new Document(firstPdfFilePath);
            // Merge the first PDF document
            mergeResultPdfDocument.AppendDocument(firstPdfDocumentToMerge);

            // Load the second PDF document to merge
            string secondPdfFilePath = Server.MapPath("~/DemoAppFiles/Input/PDF_Files/Merge_After_Conversion.pdf");
            Document secondPdfDocumentToMerge = new Document(secondPdfFilePath);
            // Merge the second PDF document
            mergeResultPdfDocument.AppendDocument(secondPdfDocumentToMerge);

            // Save the merge result PDF document in a memory buffer
            byte[] outPdfBuffer = mergeResultPdfDocument.Save();

            // Send the PDF as response to browser

            // Set response content type
            Response.AddHeader("Content-Type", "application/pdf");

            // Instruct the browser to open the PDF file as an attachment or inline
            Response.AddHeader("Content-Disposition", String.Format("attachment; filename=Merge_PDF.pdf; size={0}", outPdfBuffer.Length.ToString()));

            // Write the PDF document buffer to HTTP response
            Response.BinaryWrite(outPdfBuffer);

            // End the HTTP response and stop the current page processing
            Response.End();
        }
        finally
        {
            // Close the PDF document resulted after merge
            // When the AutoCloseAppendedDocs property is true the merged PDF documents will also be closed
            mergeResultPdfDocument.Close();
        }
    }