Add a watermark to a PDF

Stamp a diagonal text watermark like CONFIDENTIAL or DRAFT across every page of a PDF. FileAlloy watermarks PDFs through a fast, private API with tunable opacity and size: send the file and your text, get a marked PDF back. Files are processed in memory and never stored, and there is a free tier to start.

Files are processed in memory and never stored.

How to use Add a watermark to a PDF

Get a free API key Create an account at app.filealloy.com and generate a key. The free plan is enough to start.
POST your PDF and text Send the file to /v1/watermark with your key and the watermark text, plus optional opacity and size.
Get the marked PDF A PDF with a diagonal watermark on every page comes straight back in the response.

Why FileAlloy

Every page marked

A diagonal, semi-transparent text watermark is stamped across all pages in one call.

Tune it

Set the text, the opacity (0 to 1), and the font size to get exactly the look you want.

Nothing retained

The document sits in memory only while the stamp is applied, then it is discarded with the response.

Consistent on EU servers

Processing runs in the EU with no model in the loop, so one set of options always yields the same mark.

Do it at scale with the API

Marking documents as confidential or draft automatically? The same operation is a single call to /v1/watermark, so you can batch and automate it with no browser.

curl -X POST https://api.filealloy.com/v1/watermark \
  -H "X-API-Key: fa_live_your_key" \
  -F "file=@document.pdf" \
  -F "text=CONFIDENTIAL" \
  -o watermarked.pdf

Get an API key

Frequently asked questions

What does the watermark look like?

A diagonal, semi-transparent line of text across each page, like CONFIDENTIAL or DRAFT. You choose the words.

Can I control how visible it is?

Yes. Set opacity from 0 to 1 and pick a font size, so it can be subtle or bold.

Are my files stored?

No. Files are processed in memory and deleted immediately after the response.

What is the endpoint?

POST /v1/watermark with the PDF and a text field as multipart form data.

Can I watermark documents in bulk?

Call the endpoint once per file. It is stateless, so you can mark a whole batch in parallel.

Is there a free option?

Yes. The free plan includes a monthly request quota, with sub-cent pricing above it.