如何在PdfBox2中将页面原点转换为左上角？

import org.apache.pdfbox.pdmodel.PDDocument;
import org.apache.pdfbox.pdmodel.PDPage;
import org.apache.pdfbox.pdmodel.PDPageContentStream;
import org.apache.pdfbox.pdmodel.common.PDRectangle;

import java.awt.geom.AffineTransform;
import java.io.File;
import java.io.IOException;

public class PdfBoxExample {
    public static void main(String[] args) {
        try {
            // 加载PDF文档
            PDDocument document = PDDocument.load(new File("input.pdf"));

            // 获取第一页
            PDPage page = document.getPage(0);

            // 获取页面的旋转角度
            int rotation = page.getRotation();

            // 获取页面的尺寸
            PDRectangle mediaBox = page.getMediaBox();
            float pageWidth = mediaBox.getWidth();
            float pageHeight = mediaBox.getHeight();

            // 计算页面的偏移量
            float offsetX = 0;
            float offsetY = 0;
            if (rotation == 90 || rotation == 270) {
                offsetY = pageHeight;
            }

            // 转换页面内容
            PDPageContentStream contentStream = new PDPageContentStream(document, page, PDPageContentStream.AppendMode.PREPEND, false);
            AffineTransform transform = new AffineTransform();
            transform.translate(offsetX, offsetY);
            contentStream.transform(transform);
            contentStream.close();

            // 保存修改后的PDF文档
            document.save("output.pdf");
            document.close();

            System.out.println("转换完成！");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}