如何扩展PDF的页面大小以添加水印？ [英] How to extend the page size of a PDF to add a watermark?

问题描述

我的网络应用程序签署PDF文档。我想让用户下载原始PDF文档（未签名），但在pdf文档的左边缘添加图像和签名者。

My web application signs PDF documents. I would like to let users download the original PDF document (not signed) but adding an image and the signers in the left margin of the pdf document.

我见过这个想法在另一个Web应用程序中，我想做同样的事情。当然我想用itext库来做。

I've seen this idea in another web application, and I would like to do the same. Of course I would like to do it using itext library.

我附上了两张图片，原始PDF文件（未签名）和修改后的PDF文件。

I have attached two images, the original PDF document (not signed) and the modified PDF document.

推荐答案

首先：在对进行数字签名之前更改文档非常重要。一旦经过数字签名，这些更改将破坏签名。

First this: it is important to change the document before you digitally sign it. Once digitally signed, these changes will break the signature.

我将分两部分分解问题，我将跳过关于实际水印的部分，因为这已经是这里解释：如何使用文本或图像为PDF水印？

I will break up the question in two parts and I'll skip the part about the actual watermarking as this is already explained here: How to watermark PDFs using text or images?

这个问题与该问题不重复，因为额外要求在右边添加额外的保证金。

This question is not a duplicate of that question, because of the extra requirement to add an extra margin to the right.

查看 primes.pdf 文档。这是我们将在 AddExtraMargin 示例中使用的源文件，其结果如下：< a href =http://itextpdf.com/sites/default/files/primes_extra_margin.pdf =nofollow noreferrer> primes_extra_margin.pdf 。正如您所看到的，每页左侧增加了半英寸的边距。

Take a look at the primes.pdf document. This is the source file we are going to use in the AddExtraMargin example with the following result: primes_extra_margin.pdf. As you can see, a half an inch margin was added to the left of each page.

这就是它的完成方式：

public void manipulatePdf(String src, String dest) throws IOException, DocumentException {
    PdfReader reader = new PdfReader(src);
    int n = reader.getNumberOfPages();
    PdfStamper stamper = new PdfStamper(reader, new FileOutputStream(dest));
    // properties
    PdfContentByte over;
    PdfDictionary pageDict;
    PdfArray mediabox;
    float llx, lly, ury;
    // loop over every page
    for (int i = 1; i <= n; i++) {
        pageDict = reader.getPageN(i);
        mediabox = pageDict.getAsArray(PdfName.MEDIABOX);
        llx = mediabox.getAsNumber(0).floatValue();
        lly = mediabox.getAsNumber(1).floatValue();
        ury = mediabox.getAsNumber(3).floatValue();
        mediabox.set(0, new PdfNumber(llx - 36));
        over = stamper.getOverContent(i);
        over.saveState();
        over.setColorFill(new GrayColor(0.5f));
        over.rectangle(llx - 36, lly, 36, ury - llx);
        over.fill();
        over.restoreState();
    }
    stamper.close();
    reader.close();
}

PdfDictionary 我们得到 getPageN（）方法被称为页面字典。它包含有关PDF中特定页面的大量信息。我们只查看一个条目： / MediaBox 。这只是一个概念证明。如果你想编写一个更强大的应用程序，你还应该查看 / CropBox 和 / Rotate 条目。顺便说一句，我知道这些条目在primes.pdf中不存在，所以我在这里省略它们。

The PdfDictionary we get with the getPageN() method is called the page dictionary. It has plenty of information about a specific page in the PDF. We are only looking at one entry: the /MediaBox. This is only a proof of concept. If you want to write a more robust application, you should also look at the /CropBox and the /Rotate entry. Incidentally, I know that these entries don't exist in primes.pdf, so I am omitting them here.

媒体框 page是一个包含四个值的数组，表示由其左下角和右上角的坐标定义的矩形（通常，我将它们称为 llx ， lly ， urx 和 ury ）。

The media box of a page is an array with four values that represent a rectangle defined by the coordinates of its lower-left and upper-right corner (usually, I refer to them as llx, lly, urx and ury).

在我的代码示例中，我通过减去36个用户单位来更改 llx 的值。如果您比较两个PDF的页面大小，您会看到我们已经添加了半英寸。

In my code sample, I change the value of llx by subtracting 36 user units. If you compare the page size of both PDFs, you'll see that we've added half an inch.

我们还使用这些坐标绘制一个覆盖额外的半英寸。现在切换到其他水印示例，了解如何为每个页面添加文字或其他内容。

We also use these coordinates to draw a rectangle that covers the extra half inch. Now switch to the other watermark examples to find out how to add text or other content to each page.

更新：

如果您需要缩小现有页面，请阅读修正PDF的方向以便扩展它

if you need to scale down the existing pages, please read Fix the orientation of a PDF in order to scale it

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