自动识别 Excel 样式，转为 PDF 样式，可添加水印

import com.itextpdf.text.Font;
import com.itextpdf.text.*;
import com.itextpdf.text.pdf.*;
import com.itextpdf.text.pdf.interfaces.PdfViewerPreferences;
import com.itextpdf.text.pdf.internal.PdfViewerPreferencesImp;
import lombok.SneakyThrows;
import org.apache.poi.ss.usermodel.*;
import org.apache.poi.ss.util.CellRangeAddress;
import org.apache.poi.xssf.usermodel.XSSFColor;
import org.apache.poi.xssf.usermodel.XSSFFont;
import org.apache.poi.xssf.usermodel.XSSFSheet;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.math.BigDecimal;
import java.util.List;

public class ExcelToPdf {

    /**
     * 转换 Excel 为 PDF 文件
     *
     * @param workbook       excel 文档
     * @param outputStream   pdf 输出流
     * @param watermarkText1 水印文本1
     * @param watermarkText2 水印文本2
     */
    public static void convertExcelToPDF(XSSFWorkbook workbook, OutputStream outputStream, String watermarkText1, String watermarkText2) throws IOException, DocumentException {
        if (workbook.getNumberOfSheets() <= 0) {
            Document document = new Document();
            PdfWriter instance = PdfWriter.getInstance(document, outputStream);
            instance.setPageEvent(new WatermarkPageEvent(watermarkText1, watermarkText2));
            document.open();
            document.add(new Paragraph(" "));
            document.close();
            workbook.close();
            return;
        }
        // 获取 Excel 列宽度（假设第一列的宽度为 PDF 页面宽度）
        float excelColumnWidth = workbook.getSheetAt(0).getColumnWidth(0);
        Document document = new Document(new Rectangle(excelColumnWidth, 842));
        PdfWriter instance = PdfWriter.getInstance(document, outputStream);
        instance.setPageEvent(new WatermarkPageEvent(watermarkText1, watermarkText2));
        document.open();
        for (int i = 0; i < workbook.getNumberOfSheets(); i++) {
            XSSFSheet worksheet = workbook.getSheetAt(i);
            // sheet 去除密码保护
            worksheet.protectSheet("****");
            worksheet.protectSheet(null);
            createAndAddTable(worksheet, document);
            if (i < workbook.getNumberOfSheets() - 1) {
                document.newPage();
            }
        }
        document.close();
        workbook.close();
    }

    /**
     * 新增表格
     *
     * @param worksheet Excel 工作簿
     * @param document  PDF 文档
     */
    private static void createAndAddTable(XSSFSheet worksheet, Document document) throws DocumentException, IOException {
        if (worksheet.getRow(0) == null) {
            document.newPage();
            document.add(new Paragraph(" "));
            return;
        }
        // 创建表格，根据 Excel 的第一行，获取需要创建的列数
        PdfPTable table = new PdfPTable(worksheet.getRow(0).getPhysicalNumberOfCells());
        // 设置表格宽度
        table.setWidthPercentage(100);
        table.setLockedWidth(false);
        // 添加表格数据
        addTableData(worksheet, table);
        // 合并单元格
        mergeTableCell(worksheet, table);
        // 将表格加入 PDF 文档
        document.add(table);
    }

    // 合并单元格
    private static void mergeTableCell(XSSFSheet worksheet, PdfPTable table) {
        List<CellRangeAddress> mergedRegions = worksheet.getMergedRegions();
        for (CellRangeAddress mergedRegion : mergedRegions) {
            PdfPRow row = table.getRow(mergedRegion.getFirstRow());
            int mergeCell = mergedRegion.getLastColumn() - mergedRegion.getFirstColumn();
            // +1 是因为起始单元格占 1 个格子
            row.getCells()[mergedRegion.getFirstColumn()].setColspan(mergeCell + 1);
        }
    }

    // 获取 Excel 单元格内容
    public static String getCellText(Cell cell) {
        if (cell == null) {
            return "";
        }
        String cellValue;
        switch (cell.getCellTypeEnum()) {
            case STRING:
                cellValue = cell.getStringCellValue();
                break;
            case NUMERIC:
                cellValue = String.valueOf(BigDecimal.valueOf(cell.getNumericCellValue()));
                break;
            case BLANK:
            default:
                cellValue = "";
                break;
        }
        return cellValue;
    }

    // 添加表格数据
    private static void addTableData(XSSFSheet worksheet, PdfPTable table) throws DocumentException, IOException {
        for (Row row : worksheet) {
            for (int i = 0; i < row.getPhysicalNumberOfCells(); i++) {
                Cell cell = row.getCell(i);
                if (cell == null) {
                    continue;
                }
                String cellValue = getCellText(cell);
                // 创建单元格，填充文本和字体相关样式
                PdfPCell cellPdf = new PdfPCell(new Phrase(cellValue, getCellStyle(cell)));
                // 设置单元格背景色
                setBackgroundColor(cell, cellPdf);
                // 设置单元格中内容对齐方式
                setCellAlignment(cell, cellPdf);
                // 将单元格加入 PDF 中
                table.addCell(cellPdf);
            }
        }
    }

    // 设置背景
    private static void setBackgroundColor(Cell cell, PdfPCell cellPdf) {
        short bgColorIndex = cell.getCellStyle().getFillForegroundColor();
        // 是否自动背景色
        if (bgColorIndex != IndexedColors.AUTOMATIC.getIndex()) {
            XSSFColor bgColor = (XSSFColor) cell.getCellStyle().getFillForegroundColorColor();
            if (bgColor != null) {
                String argbHex = bgColor.getARGBHex();
                int argb = (int) Long.parseLong(argbHex.substring(1), 16); // 将 hex 颜色转为 rgb
                int red = (argb >> 16) & 0xFF; // 提取红色部分
                int green = (argb >> 8) & 0xFF; // 提取绿色部分
                int blue = argb & 0xFF; // 提取蓝色部分
                cellPdf.setBackgroundColor(new BaseColor(red, green, blue));
            }
        }
    }

    // 设置单元格对齐方式
    private static void setCellAlignment(Cell cell, PdfPCell cellPdf) {
        CellStyle cellStyle = cell.getCellStyle();
        HorizontalAlignment horizontalAlignment = cellStyle.getAlignmentEnum();
        VerticalAlignment verticalAlignment = cellStyle.getVerticalAlignmentEnum();
        switch (horizontalAlignment) {
            case LEFT:
                cellPdf.setHorizontalAlignment(Element.ALIGN_LEFT);
                break;
            case CENTER:
                cellPdf.setHorizontalAlignment(Element.ALIGN_CENTER);
                break;
            case JUSTIFY:
            case FILL:
                cellPdf.setVerticalAlignment(Element.ALIGN_JUSTIFIED);
                break;
            case RIGHT:
                cellPdf.setHorizontalAlignment(Element.ALIGN_RIGHT);
                break;
        }
        switch (verticalAlignment) {
            case TOP:
                cellPdf.setVerticalAlignment(Element.ALIGN_TOP);
                break;
            case CENTER:
                cellPdf.setVerticalAlignment(Element.ALIGN_MIDDLE);
                break;
            case JUSTIFY:
                cellPdf.setVerticalAlignment(Element.ALIGN_JUSTIFIED);
                break;
            case BOTTOM:
                cellPdf.setVerticalAlignment(Element.ALIGN_BOTTOM);
                break;
        }
    }

    // 获取单元格内容样式
    private static Font getCellStyle(Cell cell) throws DocumentException, IOException {
        Font font = new Font(BaseFont.createFont("STSong-Light", "UniGB-UCS2-H", true));
        CellStyle cellStyle = cell.getCellStyle();
        org.apache.poi.ss.usermodel.Font cellFont = cell.getSheet()
            .getWorkbook()
            .getFontAt(cellStyle.getFontIndex());
        // 字体颜色
        short fontColorIndex = cellFont.getColor();
        if (fontColorIndex != IndexedColors.AUTOMATIC.getIndex() && cellFont instanceof XSSFFont) {
            XSSFColor fontColor = ((XSSFFont) cellFont).getXSSFColor();
            if (fontColor != null) {
                byte[] rgb = fontColor.getRGB();
                if (rgb != null && rgb.length == 3) {
                    font.setColor(new BaseColor(rgb[0] & 0xFF, rgb[1] & 0xFF, rgb[2] & 0xFF));
                }
            }
        }
        if (cellFont.getItalic()) {
            font.setStyle(Font.ITALIC);
        }
        if (cellFont.getStrikeout()) {
            font.setStyle(Font.STRIKETHRU);
        }
        if (cellFont.getUnderline() == 1) {
            font.setStyle(Font.UNDERLINE);
        }
        // 设置字体大小
        short fontSize = cellFont.getFontHeightInPoints();
        font.setSize(fontSize);
        if (cellFont.getBold()) {
            font.setStyle(Font.BOLD);
        }
        // 设置字体
        String fontName = cellFont.getFontName();
        if (FontFactory.isRegistered(fontName)) {
            font.setFamily(fontName);
        } else {
            font.setFamily("Helvetica");
        }
        return font;
    }
}

WatermarkPageEvent 水印

import cn.hutool.core.util.StrUtil;
import com.itextpdf.text.*;
import com.itextpdf.text.pdf.*;
import lombok.SneakyThrows;

public class WatermarkPageEvent extends PdfPageEventHelper {

    /**
     * 水印1
     */
    Phrase watermark1;

    /**
     * 水印2
     */
    Phrase watermark2;

    Font font;

    @SneakyThrows
    public WatermarkPageEvent(String watermarkText1, String watermarkText2) {
        font = new Font(BaseFont.createFont("STSong-Light", "UniGB-UCS2-H", true), 15);
        font.setColor(new BaseColor(192, 192, 192, 255));
        if (StrUtil.isNotBlank(watermarkText1)) {
            watermark1 = new Phrase(watermarkText1, font);
        }
        if (StrUtil.isNotBlank(watermarkText2)) {
            watermark2 = new Phrase(watermarkText2, font);
        }
    }

    @Override
    public void onEndPage(PdfWriter writer, Document document) {
        float height = document.getPageSize().getHeight();
        float width = document.getPageSize().getWidth();
        PdfContentByte directContentUnder = writer.getDirectContentUnder();
        if (watermark1 != null) {
            for (int y = 200; y <= height; y += 400) {
                for (int x = 100; x <= width; x += 200) {
                    ColumnText.showTextAligned(directContentUnder, Element.ALIGN_CENTER, watermark1, x, y, 45);
                    ColumnText.showTextAligned(directContentUnder, Element.ALIGN_CENTER, watermark1, x, y, 45);
                    ColumnText.showTextAligned(directContentUnder, Element.ALIGN_CENTER, watermark1, x, y, 45);
                }
            }
        }
        if (watermark2 != null) {
            for (int y = 180; y <= height; y += 400) {
                for (int x = 110; x <= width; x += 200) {
                    ColumnText.showTextAligned(directContentUnder, Element.ALIGN_CENTER, watermark2, x, y, 45);
                    ColumnText.showTextAligned(directContentUnder, Element.ALIGN_CENTER, watermark2, x, y, 45);
                    ColumnText.showTextAligned(directContentUnder, Element.ALIGN_CENTER, watermark2, x, y, 45);
                }
            }
        }
    }

}