如何在itext7 C #中将页面大小从A3缩放到A4？

using iText.Kernel.Pdf;
using iText.Layout;
using iText.Layout.Element;
using iText.Layout.Properties;

PdfReader reader = new PdfReader("source.pdf");

PdfWriter writer = new PdfWriter("modified.pdf");

PdfDocument document = new PdfDocument(reader, writer);

int pageCount = document.GetNumberOfPages();

for (int i = 1; i <= pageCount; i++)
{
    // 获取当前页面
    PdfPage page = document.GetPage(i);
    
    // 创建一个新的A4大小
    PageSize a4 = PageSize.A4;
    
    // 设置当前页面大小为A4
    page.SetPageSize(a4);
    
    // 更新页面内容
    PdfCanvas canvas = new PdfCanvas(page);
    canvas.ConcatMatrix(a4.GetWidth() / PageSize.A3.GetWidth(), 0, 0, a4.GetHeight() / PageSize.A3.GetHeight(), 0, 0);
}

document.Close();