Question 1

How do I add a watermark to a PDF online?

Accepted Answer

Upload your PDF file. Enter the watermark text (e.g. CONFIDENTIAL), set the opacity with the slider, and choose the position (center, diagonal, or bottom corner). Click "Add watermark". The tool adds the text to every page using pdf-lib in your browser, then you download the result. Everything runs in your browser; no data is sent to any server.

Question 2

Are my PDFs sent to a server?

Accepted Answer

No. Watermarking is done in your browser using pdf-lib. Your PDF never leaves your device.

Question 3

Can I change the watermark text?

Accepted Answer

Yes. Before clicking Add watermark, type any text in the watermark field. The default is "CONFIDENTIAL". You can use any short phrase or word.

Question 4

What does the opacity slider do?

Accepted Answer

The slider controls how light or dark the watermark appears. Lower values make the text more subtle (lighter gray); higher values make it more visible. The tool uses gray color; the slider adjusts the intensity so the watermark does not overwhelm the content.

Question 5

What position options are there?

Accepted Answer

You can place the watermark in the center of each page, diagonally across the page (rotated 45°), or in the bottom corner. Choose the option that best fits your document layout.

Question 6

Does it work with password-protected PDFs?

Accepted Answer

Password-protected PDFs must be unlocked first. Open the PDF with the correct password in another app, save without password, then use that copy here.

Question 7

Does it work on mobile?

Accepted Answer

Yes. The tool runs in the mobile browser. Upload your PDF, set the watermark options, add the watermark, and download. No app install required.

Question 8

Is there a page limit?

Accepted Answer

There is no fixed limit. Very long PDFs may take longer and use more memory. For typical documents (e.g. under 100 pages), watermarking works well.

Question 9

Can I remove a watermark later?

Accepted Answer

This tool only adds watermarks. It does not remove existing watermarks. If you need to remove a watermark, you would need a PDF editor that supports editing or removing overlay content.

Question 10

What font is used for the watermark?

Accepted Answer

The tool uses the standard Helvetica font (built into PDF). The text is drawn as vector text so it stays sharp at any zoom level.

免费在线为 PDF 添加水印

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