Watermark a PDF without uploading it: methods and limits

What is a watermark for, and what isn't it for?

A watermark is a semi-transparent text repeated on every page: “Sent to Mr Martin, for use in the proceedings only”, “Copy for agency X, rental of 12 rue…”. It does three things:

• It discourages reuse. An ID card marked “for the rental of property X” is hard to reuse to open an account elsewhere. That's why French public services recommend marking the copies you send.
• It reminds the recipient, and anyone they forward it to, of the intended use.
• It helps trace a leak, if each recipient received a differently marked copy.

What a watermark does not do is make anything unreadable. The card number, the address, the salary are still visible under the transparent text. If a piece of information must not be shared at all, it has to be removed from the document: that's redaction, explained in redact a PDF. The two combine well: redact what is none of the recipient's business, then watermark what they receive.

The CNIL, the French data protection authority, takes the same line for businesses that keep copies of ID documents: in its reference framework on managing commercial activities, it lists among reinforced security measures adding a watermark showing the collection date and the identity of the controller, to prevent misuse such as using the photos for facial recognition.

What should a watermark say?

Cybermalveillance.gouv.fr advises systematically marking copies of your documents before sending them, stating the purpose of the transfer, the date and the recipient. Those three elements are enough:

No need to type the date: in AnonymFiles, the “Add today’s date” box appends it to the text, in DD/MM/YYYY format. A few practical rules:

• Keep it short. The text is limited to 120 characters, and the longer it is, the more it is shrunk to fit on the page.
• No square brackets. The app refuses them, because they are used for pseudonymization placeholders such as [PERSONNE_1].
• No unusual characters. PDF watermarks use the format's standard fonts, which cover the Latin alphabet: long dashes, curly quotes and ellipses are rendered as their plain equivalents, “€” becomes “EUR” and “œ” becomes “oe”; emojis are refused.
• No unnecessary personal data. The recipient's name is enough; there's no need to add your own phone number.

How does Filigrane Facile, the French government service, work?

Filigrane Facile (filigrane.beta.gouv.fr) is a free public service published by the Direction générale de l'aménagement, du logement et de la nature (DGALN), the French housing and planning directorate, and run by the DossierFacile team. According to its terms of use, accessed on October 20, 2026:

• it accepts JPG, PNG, HEIC and PDF files and always returns a PDF;
• you choose your file, type the text, then download the watermarked copy, one file at a time;
• the publisher undertakes to delete the original files once the watermarked file is generated, and the watermarked file after the first download, or after one day if it hasn't been downloaded;
• the site is hosted by OVH, and the service states that it does not guarantee the authenticity of the document.

The service suggests “Document exclusivement destiné à la location immobilière” (document intended exclusively for a property rental) as sample text, and warns that some organizations, such as banks or public services, may need a blank document. Both the CNIL and Cybermalveillance.gouv.fr point people to it.

It's the right reflex for an individual sending a document now and then. Its only drawback, given the goal of not uploading anything, is one of principle: the file passes through a server, even if it is deleted quickly. For documents covered by professional secrecy, or to watermark a whole case file, a local tool avoids that step.

Is the watermark burned into the pixels?

It depends on the tool. There are three ways to add a watermark to a PDF, and they don't offer the same resistance:

AnonymFiles uses the second technique. The watermark is written into the content of the PDF pages, on top of everything else, and not as an annotation a reader could hide. On a scan, it is placed over the page image: it is not merged into its pixels. The document's text therefore stays selectable and readable by an AI or a search engine, and the file barely grows. The flip side is that someone equipped and determined can remove that text with a PDF editor. Some software makes the opposite choice: Anoni, for example, says in its guide that it turns each page into an image to embed the mark, at the cost of non-selectable text and a heavier file.

In a Word document, the watermark is WordArt placed in the headers, behind the text, on every page, including a different first page or even pages. A Word file remains editable by its recipient: according to Microsoft, Word's Document Inspector finds and removes headers, footers and watermarks. For a copy that needs to hold up, send a PDF.

Tiled or centered, and how strong?

In AnonymFiles, the “Intensity” setting offers three presets and a “Custom” mode. The three presets repeat the text in a tiled pattern, at a 45° angle, in gray:

The layout is chosen in “Custom” mode: “Tiled” or “Once, in the centre”. The tiled pattern, built out from the center of the page in staggered rows, covers the whole surface: it's the most dissuasive option, since cropping the page won't get rid of it. The centered option suits documents where the watermark should get in the way of reading as little as possible, such as a plan or a dense invoice.

Either way, the size adjusts automatically: if the text is too long for the page, it is reduced so that one complete, angled occurrence fits within 90% of the page. Pages rotated by 90° or 180° get the watermark the right way up.

How do you watermark a PDF with AnonymFiles?

There are two routes, depending on whether you start from a ready copy or from a case file you are redacting.

On a chosen copy, such as a supporting document or an already redacted PDF:

1. Open Settings › Watermark. The “Distribution watermark” window appears.
2. Enter the “Watermark text” and, if you want to look it up later, the “Recipient”: that name is “Kept in the private register, never on the copy.”
3. Choose the “Intensity”, tick “Add today’s date” if needed, and leave “Tracing code on every page” ticked.
4. Click “Choose the copy to watermark…” and select a PDF or Word (.docx) file of up to 50 MiB.
5. Save the copy: the app suggests “file name - watermarked.pdf” next to the original, which it never modifies or overwrites. The message “Watermarked copy saved. Tracing code: …” gives the assigned code, and “Show the file” opens its folder.

When exporting a redacted case file: in Export › “To send to someone”, expand “Options” and tick “Watermark PDF and Word files”. The same form appears, and every PDF and Word file in the export gets the watermark, including PDFs produced from text documents. Text copies intended for an AI are never watermarked.

The watermark is applied after redaction and only adds content: nothing that was removed is restored. JPG or PNG images aren't accepted directly: save them as a PDF first.

How can you tell which copy leaked?

If you send the same document to three people with the same watermark, a copy that resurfaces doesn't tell you which of the three passed it on. Hence the tracing code:

• a neutral 8-character code, such as 7K3Q-92XD, with a check character and without the letters I, L, O and U to avoid confusion;
• printed discreetly at the bottom right of every page (in the footer for a Word file), and repeated in the file's metadata;
• drawn afresh for each recipient: two transfers, two codes.

The register linking each code to its recipient, the date and the documents sent, with their SHA-256 fingerprints, is encrypted on the computer and never leaves it. To trace a copy, open Settings › Watermark, “Look up a code” section, enter the code printed at the bottom of the page and click “Look up”; the field tolerates upper or lower case, spaces, and mix-ups between O and 0 or between I, L and 1. The “Codes already issued” list summarizes past transfers.

Two limits to keep in mind: the code identifies the copy that was handed over, not the person who forwarded it; and, like the watermark, it can be erased by someone who takes the trouble. No invisible watermark is inserted into the text: invisible characters would get in the way of an AI reading the document.

Does the watermark add the software's branding?

No. The watermark contains only your text and, if you ask for it, the neutral code. Neither the AnonymFiles name nor its logo appears, on the page or in the metadata: the fields that usually name the software that produced a PDF are emptied, and so are those of a Word file. That matters when the document goes to opposing counsel, a client or a public body: it's your document, not an advert. For more on this hidden data, see remove PDF metadata.

Which method should you choose?

For an individual watermarking three supporting documents, Filigrane Facile is the simplest answer, and it's free. AnonymFiles is for professionals who regularly pass on confidential documents: lawyers, notaries, accountants, HR departments or local authorities disclosing documents after redaction (see CADA requests: redact before you disclose). Pricing is on the pricing page, and the professions concerned on pages such as lawyers.