如何将现有的A4 PDF文档转换为A5小册子？

Question

我正在尝试使用itext将A4 pdf转换为A5小册子格式pdf，但未按照A5格式转换。任何人都建议如何做，这将对您大有帮助。

public void manipulatePdf(String src, String dest)
        throws IOException, DocumentException {
    // Creating a reader
    PdfReader reader = new PdfReader(src);
    // step 1
    Document document = new Document(PageSize.A5.rotate());
    // step 2
    PdfWriter writer
            = PdfWriter.getInstance(document, new FileOutputStream(dest));
    // step 3
    document.open();
    // step 4
    PdfContentByte canvas = writer.getDirectContent();
    float a4_width = PageSize.A4.getWidth();
    int n = reader.getNumberOfPages();
    int p = 0;
    PdfImportedPage page;
    while (p++ < n) {
        page = writer.getImportedPage(reader, p);
        if (p % 2 == 1) {
            canvas.addTemplate(page, 0, 0);
        } else {
            canvas.addTemplate(page, a4_width, 0);
            document.newPage();
        }
    }
    // step 5
    document.close();
    reader.close();
}