如何添加水印到PDF文件？

问题描述

我使用C＃和iTextSharp的添加水印到我的PDF文件：

I'm using C# and iTextSharp to add a watermark to my PDF files:

Document document = new Document();
PdfReader pdfReader = new PdfReader(strFileLocation);
PdfStamper pdfStamper = new PdfStamper(pdfReader, new FileStream(strFileLocationOut, FileMode.Create, FileAccess.Write, FileShare.None));
iTextSharp.text.Image img = iTextSharp.text.Image.GetInstance(WatermarkLocation);
img.SetAbsolutePosition(100, 300);
PdfContentByte waterMark;
//
for (int pageIndex = 1; pageIndex <= pdfReader.NumberOfPages; pageIndex++)
{
    waterMark = pdfStamper.GetOverContent(pageIndex);
    waterMark.AddImage(img);
}
//
pdfStamper.FormFlattening = true;
pdfStamper.Close();

它工作正常，但我的问题是，在某些PDF文件没有水印添加，虽然文件大小增加，任何想法？

It works fine, but my problem is that in some PDF files no watermark is added although the file size increased, any idea?

推荐答案

事实上，文件大小增加是一个很好的迹象，水印添加。主要的问题是，您要添加的页面的可视区域之外的水印。见How利用iText以相对文本位置页？

The fact that the file size increases is a good indication that the watermark is added. The main problem is that you're adding the watermark outside the visible area of the page. See How to position text relative to page using iText?

您需要的是这样的：

Rectangle pagesize = reader.GetCropBox(pageIndex);
if (pagesize == null)
    pagesize = reader.GetMediaBox(pageIndex);
img.SetAbsolutePosition(
    pagesize.GetLeft(),
    pagesize.GetBottom());

即：如果要在页面的左下角添加的图片。可以添加的偏移，但要确保在x方向上的偏移量不超过页面的宽度，并在y方向上的偏移量不超过页的高度。

That is: if you want to add the image in the lower-left corner of the page. You can add an offset, but make sure the offset in the x direction doesn't exceed the width of the page, and the offset in the y direction doesn't exceed the height of the page.

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