示例代码：

import org.apache.pdfbox.pdmodel.PDDocument;
import org.apache.pdfbox.rendering.PDFRenderer;

import javax.imageio.ImageIO;
import java.awt.*;
import java.awt.geom.AffineTransform;
import java.awt.image.BufferedImage;
import java.awt.image.ColorModel;
import java.awt.image.WritableRaster;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;

/**
 * @Author: Mr.Liang
 * @CreateTime: 2022-11-26  09:33
 * @Description: pdf转图片
 **/
public class Test3 {

    public static void main(String[] args) throws Exception {
        Test3 test = new Test3();
        test.pdfToImage();
    }

    /**
     * pdf转图片方式1
     */
    public void pdfToImage() {
        File file = new File("D:\\uploadPic\\test02.pdf");
        try {
            PDDocument document = PDDocument.load(file);
            PDFRenderer renderer = new PDFRenderer(document);
            for (int i = 0; i < document.getNumberOfPages(); i++) {
                // dpi 设置越大 图片越大越清晰
                BufferedImage bufferedImage = renderer.renderImageWithDPI(i, 100);
                //BufferedImage newImg = null;
                // copy原来的图片
                //newImg = new BufferedImage(bufferedImage.getWidth(), bufferedImage.getHeight(), BufferedImage.TYPE_BYTE_GRAY);
                //newImg.getGraphics().drawImage(bufferedImage.getScaledInstance(bufferedImage.getWidth(), bufferedImage.getHeight(), Image.SCALE_SMOOTH), 0, 0, null);
                bufferedImage = rotateImage(bufferedImage, 90);
                // 自定义长宽
//                BufferedImage img = resize(bufferedImage, 1190, 1684);
                // 图片要写入的地址
                File picFile = new File("D:\\uploadPic\\", "test02.png");
                OutputStream outputStream = new FileOutputStream(picFile);
                // 注意 png 比 jpg 更清晰
                ImageIO.write(bufferedImage, "png", outputStream);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }


    // 旋转图片
    public static BufferedImage rotateImage(Image src, int angel) {
        int src_width = src.getWidth(null);
        int src_height = src.getHeight(null);
        Rectangle rect_des = calcRotatedSize(new Rectangle(new Dimension(src_width, src_height)), angel);
        BufferedImage bufferedImage = new BufferedImage(rect_des.width, rect_des.height, BufferedImage.TYPE_INT_RGB);
        Graphics2D g2 = bufferedImage.createGraphics();
        // 平移
        g2.translate((rect_des.width - src_width) / 2, (rect_des.height - src_height) / 2);
        // 旋转变换
        g2.rotate(Math.toRadians(angel), src_width / 2, src_height / 2);
        g2.drawImage(src, null, null);
        g2.dispose();
        return bufferedImage;
    }

    // 计算旋转后的图片大小
    private static Rectangle calcRotatedSize(Rectangle src, int angel) {
        // 如果旋转的角度大于90度，需要进行转换
        if (angel >= 90) {
            if (angel / 90 % 2 == 1) {
                int temp = src.height;
                src.height = src.width;
                src.width = temp;
            }
            angel = angel % 90;
        }
        double r = Math.sqrt(src.height * src.height + src.width * src.width) / 2;
        double len = 2 * Math.sin(Math.toRadians(angel) / 2) * r;
        double angel_alpha = (Math.PI - Math.toRadians(angel)) / 2;
        double angel_dalta_width = Math.atan((double) src.height / src.width);
        double angel_dalta_height = Math.atan((double) src.width / src.height);

        int len_dalta_width = (int) (len * Math.cos(Math.PI - angel_alpha - angel_dalta_width));
        int len_dalta_height = (int) (len * Math.cos(Math.PI - angel_alpha - angel_dalta_height));
        int des_width = src.width + len_dalta_width * 2;
        int des_height = src.height + len_dalta_height * 2;
        return new Rectangle(new Dimension(des_width, des_height));
    }

    private static BufferedImage resize(BufferedImage source, int targetW, int targetH) {
        int type = source.getType();
        BufferedImage target = null;
        double sx = (double) targetW / source.getWidth();
        double sy = (double) targetH / source.getHeight();
        if (sx > sy) {
            sx = sy;
            targetW = (int) (sx * source.getWidth());
        } else {
            sy = sx;
            targetH = (int) (sy * source.getHeight());
        }
        if (type == BufferedImage.TYPE_CUSTOM) {
            ColorModel cm = source.getColorModel();
            WritableRaster raster = cm.createCompatibleWritableRaster(targetW, targetH);
            boolean alphaPremultiplied = cm.isAlphaPremultiplied();
            target = new BufferedImage(cm, raster, alphaPremultiplied, null);
        } else {
            target = new BufferedImage(targetW, targetH, type);
        }
        Graphics2D g = target.createGraphics();
        g.setRenderingHint(RenderingHints.KEY_RENDERING, RenderingHints.VALUE_RENDER_QUALITY);
        g.drawRenderedImage(source, AffineTransform.getScaleInstance(sx, sy));
        g.dispose();
        return target;
    }


}