How to split PDF files from A4 size to letter size (half of A4 size) C# with Itext library

I want to split a pdf file from A4 size to letter size in c# Now i'm split it with this code , but it remains the same size

        string inPDF = Application.StartupPath + "\\log\\input.pdf";
        string outPDF = Application.StartupPath + "\\log\\output.pdf";\
        PdfStream pdfStream = new PdfStream(inPDF, FileMode.Open);
        PdfStream newPdfStream = new PdfStream(outPDF, FileMode.Create);
        PdfReader reader = new PdfReader(pdfStream);
        PageSize = reader.getPageSize(1);
        Document document = new Document(PageSize);
        PdfWriter writer = PdfWriter.getInstance(document, newPdfStream);
        document.open();
        PdfContentByte content = writer.Directcontent();
        PdfImportPage page = writer.getImportPage(reader, 1);
        content.addTemplate(page , 0 , 0);
        content.Fill();
        document.setPageSize(PageSize);
        document.Close();
        reader.Close();

• This is the original pdf file

• This is Output Pdf file expecte

How can I split pdf file to small size with half of A4 size ??? Thank for read my post !