How do i change PDF version to 1.4 using iTextSharp

[koolprasad2003]

Hello all
I have a PDF file with version 1.5, I want to change its version to 1.4 using iTextSharp, I tried with following code but failed to change the version, How can I do it
Here is my code to change the version

            string szFile = @"D:\\kk.pdf";

            using (PdfReader reader = new PdfReader(@"C:\\OCR.pdf"))
            {

                using (PdfStamper stamper = new PdfStamper(reader, new FileStream(szFile, FileMode.Create)))
                {
                    stamper.Writer.SetPdfVersion(PdfWriter.PDF_VERSION_1_4);

                }
            }

Code executed successfully but PDF version remain unchanged,

Thanks in advance
koolprasad2003