打开PDF文件时，在文件上面加一组随机码的水印
在打开PDF文件时，怎么才能做到放一组随机数据以水印的形式添加在文件中。
[解决办法]
itextsharp

PdfReader reader = new PdfReader("C:/PDF/Test.pdf");
        PdfStamper stamp = new PdfStamper(reader, new FileStream("C:/PDF/Test.pdf", FileMode.Create));
        int n = reader.NumberOfPages;
        int i = 0;
        PdfContentByte under;
        iTextSharp.text.Image im = iTextSharp.text.Image.GetInstance("C:/Image/123.jpg");
        im.SetAbsolutePosition(440, 730);
        im.ScaleAbsolute(160, 60);

        while (i < n)
        {
            i++;
            under = stamp.GetOverContent(i);
            under.AddImage(im);
        }
        stamp.Close();
        reader.Close(); 

[解决办法]
参考我之前的代码
static void waterMark(String inputFile, String outputFile,String userPassWord, String ownerPassWord, String waterMarkName, int permission)

{
try {
PdfReader reader = new PdfReader(inputFile);
PdfStamper stamper = new PdfStamper(reader, new FileOutputStream( outputFile));
// 设置密码
stamper.setEncryption(userPassWord.getBytes(), ownerPassWord.getBytes(), permission, false);
BaseFont base = BaseFont.createFont("STSong-Light", "UniGB-UCS2-H",BaseFont.NOT_EMBEDDED);
int total = reader.getNumberOfPages() + 1;
Image image = Image.getInstance(imageFilePath);
image.setAbsolutePosition(200, 400);
PdfContentByte under;
int j = waterMarkName.length();
char c = 0;
int rise = 0;
for (int i = 1; i < total; i++) {

rise = 500;
under = stamper.getUnderContent(i);
// 添加图片
// under.addImage(image);
under.beginText();
under.setColorFill(Color.CYAN);
under.setFontAndSize(base, 30);
// 设置水印文字字体倾斜 开始
if (j >= 15) {
under.setTextMatrix(200, 120);
for (int k = 0; k < j; k++) {
under.setTextRise(rise);
c = waterMarkName.charAt(k);
under.showText(c + "");
rise -= 20;
}
} else {
under.setTextMatrix(180, 100);
for (int k = 0; k < j; k++) {
under.setTextRise(rise);
c = waterMarkName.charAt(k);
under.showText(c + "");
rise -= 18;
}
}
// 字体设置结束

under.endText();
// 画一个圆
// under.ellipse(250, 450, 350, 550);
// under.setLineWidth(1f);
// under.stroke();
}
stamper.close();
} catch (Exception e) {
e.printStackTrace();
}
}