一行水印

/**
     * @param inputFile 你的PDF文件地址
     * @param outputFile 添加水印后生成PDF存放的地址
     * @param waterMarkName 你的水印
     * @return
     */
      public static boolean waterMark(String inputFile,String outputFile, String waterMarkName)
      {
        try {
            PdfReader reader = new PdfReader(inputFile);
            PdfStamper stamper = new PdfStamper(reader, new FileOutputStream(outputFile));
            //这里的字体设置比较关键，这个设置是支持中文的写法
            BaseFont base = BaseFont.createFont("STSong-Light","UniGB-UCS2-H", BaseFont.NOT_EMBEDDED);// 使用系统字体
            int total = reader.getNumberOfPages() + 1;
            PdfContentByte under;
            Rectangle pageRect = null;
            for (int i = 1; i < total; i++) 
            {
                pageRect = stamper.getReader().getPageSizeWithRotation(i);
                // 计算水印X,Y坐标
                float x = pageRect.getWidth()/2;
                float y = pageRect.getHeight()/2;
                // 获得PDF最顶层
                under = stamper.getOverContent(i);
                under.saveState();
                // set Transparency
                PdfGState gs = new PdfGState();
                // 设置透明度为0.2
                gs.setFillOpacity(0.2f);
                under.setGState(gs);
                under.beginText();
                under.setFontAndSize(base, 40);
                under.setColorFill(BaseColor.GRAY);
                // 水印文字成45度角倾斜
                under.showTextAligned(Element.ALIGN_CENTER , waterMarkName, x,y, 55);
                // 添加水印文字
                under.endText();
                under.setLineWidth(1f);
                under.stroke();
                under.restoreState();
            }
            stamper.close();
            return true;
        } catch (Exception e) {
            e.printStackTrace();
            return false;
        }
    }

两行多行水印可以这样

import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.OutputStream;

import com.itextpdf.text.BaseColor;
import com.itextpdf.text.Element;
import com.itextpdf.text.Font;
import com.itextpdf.text.Rectangle;
import com.itextpdf.text.pdf.BaseFont;
import com.itextpdf.text.pdf.PdfContentByte;
import com.itextpdf.text.pdf.PdfGState;
import com.itextpdf.text.pdf.PdfReader;
import com.itextpdf.text.pdf.PdfStamper;
/**
		 * app检测报告加水印
		 *
		 * @author: liuhy
		 * @param inputStream 输入流
		 * @param outputStream 输出流
		 * @param waterMarkName1 水印文字1
		 * @param waterMarkName2 水印文字2
		 * @return
		 */
      public static boolean apptReportWaterMark(InputStream inputStream,OutputStream outputStream, String waterMarkName1,String waterMarkName2)
      {
        try {
            PdfReader reader = new PdfReader(inputStream);
            PdfStamper stamper = new PdfStamper(reader, outputStream);
            BaseFont base = BaseFont.createFont(BaseFont.HELVETICA_BOLD, BaseFont.CP1252, BaseFont.EMBEDDED);
            
            //这里的字体设置比较关键，这个设置是支持中文的写法
//            BaseFont base = BaseFont.createFont("STSong-Light","UniGB-UCS2-H", BaseFont.NOT_EMBEDDED);// 使用系统字体
            int total = reader.getNumberOfPages() + 1;
            PdfContentByte under;
            Rectangle pageRect = null;
            for (int i = 1; i < total; i++) 
            {
                pageRect = stamper.getReader().getPageSizeWithRotation(i);
                // 计算水印X,Y坐标
                float x = pageRect.getWidth()/2;
                float y = pageRect.getHeight()/2;
                // 获得PDF最顶层
                under = stamper.getOverContent(i);
                under.saveState();
                // set Transparency
                PdfGState gs = new PdfGState();
                // 设置透明度为0.2
                gs.setFillOpacity(0.2f);
                under.setGState(gs);
                //****第一行水印开始
                under.beginText();
                under.setFontAndSize(base, 60);
                under.setColorFill(BaseColor.GRAY);
                // 水印文字成45度角倾斜
                under.showTextAligned(Element.ALIGN_CENTER , waterMarkName1, x,y+50, 20);
                // 添加水印文字
                under.endText();
                //****第一行水印结束
                //****第二行水印开始
                under.beginText();
                under.setFontAndSize(base, 36);
                under.setColorFill(BaseColor.GRAY);
                // 水印文字成45度角倾斜
                under.showTextAligned(Element.ALIGN_CENTER , waterMarkName2, x,y, 20);
                // 添加水印文字
                under.endText();
                //****第二行水印结束
                under.setLineWidth(1f);
                under.stroke();
                under.restoreState();
            }
            stamper.close();
            return true;
        } catch (Exception e) {
            e.printStackTrace();
            return false;
        }
    }

 maven

<dependency>
            <groupId>com.itextpdf</groupId>
            <artifactId>itextpdf</artifactId>
            <version>5.5.12</version>
        </dependency>
        <dependency>
            <groupId>com.itextpdf.tool</groupId>
            <artifactId>xmlworker</artifactId>
            <version>5.5.12</version>
        </dependency>
        <dependency>
            <groupId>com.itextpdf</groupId>
            <artifactId>itext-asian</artifactId>
            <version>5.2.0</version>
</dependency>