添加水印
在每一页上盖上文本或图像。
这款工具完全在你的浏览器中运行。文件从不上传，你可以在浏览器的网络标签中亲自验证这一点。 亲自验证：打开浏览器的网络标签观察。你会看到一个查询你是否还有剩余任务的小请求，只包含工具名称和一段哈希，绝不会包含文件。
这款工具的作用
This draws a mark on each page: either text you type or an image you drop alongside the document. Drawing over the existing content appends to each page and leaves links, form fields and annotations intact; drawing behind it has to recompose the page, which does not. The default is 20 percent opacity at -45 degrees through the centre.
Use it when the status of a document matters as much as its contents: a DRAFT that must not be quoted, a CONFIDENTIAL circulation, a SAMPLE for a prospective client, or photographs going out with your studio name across them.
工作原理
- Drop the PDF onto this page. For an image watermark, drop the PNG or JPEG alongside it.
- Choose text or image, and type the wording if it is text.
- Set the position, angle and opacity. Below about 25 percent the document underneath stays comfortable to read.
- Turn on Tile to repeat a text mark across the page, which is far harder to crop away.
- Choose whether the mark goes over the content or behind it, and give a page range if only some pages need it.
- Press Add watermark and the download starts.
Over and behind are not two settings of the same thing. Drawing over appends to the page's existing content stream, so the page object survives and every link, annotation and form field on it survives with it. A content stream can only be appended to, so drawing behind means recomposing the page with the mark underneath and the original content drawn back on top - which leaves the old page object, and everything attached to it, behind. If the document has fillable fields you care about, stamp over and lower the opacity instead.
Behind has a second catch: it shows through only where the page is transparent. Many documents paint an opaque white rectangle across the sheet before drawing anything else, and a mark under that is a mark nobody will ever see. If behind produces a blank-looking result, that is why.
Tiling repeats a text mark across the page, spaced at six times the type size horizontally and four times vertically, so it reads as a pattern rather than a grey wash. A tiled mark ignores the position setting, since it covers the whole sheet, and it is clipped at the page edge. Tiling applies to text only; an image is placed once.
An image watermark is placed at its natural size, reading its pixels at 96 per inch - the same assumption Image to PDF makes, so a logo lands the same size in both tools. Rotation and opacity apply to it as they do to text, and PNG transparency is kept: a logo in a white square looks like a mistake. The image, like the document, is read from your disk and never sent anywhere.
这款工具做不到的事
- A watermark is a label, not a protection. Anyone who has the file can crop it off, cover it, or convert the pages to images and start again. Use Protect PDF if you need a password or usage restrictions.
- Placing the mark behind the content recomposes every page, so links, form fields and annotations on the original are not carried across - and a page with an opaque background will hide the mark entirely.
常见问题
- 别人能移除水印吗？
- 费点功夫的话，能——它是绘制进页面的，而不是锁定在页面上的，任何有决心的人都可以裁掉它、盖住它，或重建页面。水印告诉诚实的收件人这份文档处于什么状态；它拦不住不诚实的人。平铺会让移除麻烦得多，而保护 PDF 才是用于真正限制的工具。
- 我怎样用自己的徽标而不是文本？
- 把 PNG 或 JPEG 与 PDF 一起拖到页面上，并把类型切换为图像。徽标以其自然尺寸放置，按每英寸 96 像素读取其像素，旋转和不透明度像对文本一样适用。PNG 透明度会保留，所以徽标是落在页面上，而不是落在一个白框里。
- 水印该放在文本之上还是之后？
- 大多数情况下放在之上。它保留文档的链接、表单字段和批注，在 20% 不透明度下，下面的文字读起来毫无问题。之后会重建每一页，丢失那些交互部分，而且如果文档自己画了白色背景（很多都会），它就会完全消失。
- 我能只给部分页面加水印吗？
- 可以。在高级选项中给出一个页面范围：1 表示只有封面，2- 表示除封面外的一切，或 1, 5-7, last 表示混合。范围之外的页面会原样复制。
- 我的文档和徽标会被上传吗？
- 都不会。两者都是从你的磁盘读入浏览器内存，由 pdf-lib 在 Web Worker 中盖印，再在本地写出。路径中没有服务器，所以一份被标记为机密的机密文档不会先跑到任何地方。