iText7:如何在最后一页的底部添加文本？

PdfDocument pdfDoc = new PdfDocument(new PdfReader("input.pdf"), new PdfWriter("output.pdf"));

int totalPages = pdfDoc.getNumberOfPages();

PdfPage lastPage = pdfDoc.getPage(totalPages);

PdfCanvas canvas = new PdfCanvas(lastPage, true);

canvas.setFontAndSize(PdfFontFactory.createFont(), 12);
canvas.setFillColor(Color.BLACK);

canvas.beginText();
canvas.showTextAligned(new Paragraph("底部文本"), lastPage.getPageSize().getWidth() / 2, 20, TextAlignment.CENTER);
canvas.endText();

pdfDoc.close();