PDF Watermarker for Confidential Text Overlays
A draft that leaves the office without a label is easy to lose track of once it is printed and passed around. This page stamps your own text onto the pages of a PDF with pdf-lib, running entirely inside the browser so the document never leaves the machine. Type a word such as CONFIDENTIAL, pick a tiled diagonal, centered, or header layout, set how dark the stamp should be, and choose which pages to mark. The result downloads as a new file with your stamps drawn into each selected page.
Add Text Watermarks to Any Page
Choose a PDF
Pick one file. Encrypted or damaged files are reported when you press Watermark PDF.
Watermark settings
How It Works
The file is read into a byte array with the File API and opened with pdf-lib. One Helvetica Bold font is embedded into the document before any page is touched, so every stamp shares the same font resource and the output stays small. The producer field is set to FlowStack Tools so the file names its origin in the document properties.
The page box accepts ranges such as 1-3,5 and is checked against the real page count; an empty box marks every page. For each selected page, the layout function works out where the stamps sit. Centered places one stamp at the middle of the page with a size scaled from the page width and the length of your text. Header puts a single line near the top edge. Tiled diagonal covers the page with a grid whose steps come from an estimate of the text width, and alternate rows shift sideways by half a step so the stamps do not line up in columns.
Each stamp is drawn with the drawText operator at the size, position, and rotation the layout computed. Rotation arrives in degrees and is written into the content stream as a rotation matrix, which pdf-lib builds from the angle in radians. The x coordinate is centered by measuring the real width of the string with the embedded font and subtracting half of it from the stamp position. Opacity from the slider is clamped between 5 and 100 percent and applied per stamp, then the document is serialized to bytes and handed to a local download link.
Before and After
file: board-minutes.pdf
6 pages of plain text
no mark shows who holds the copyWatermarked 6 pages with a tiled diagonal stamp
CONFIDENTIAL repeats across every sheet
[ Download watermarked.pdf ]slider at 5%
stamp nearly invisible on a printed sheet
readers miss the labelWatermarked 6 pages with a header stamp
one clear line above the body text
page content stays readableUse Cases
| Scenario | Settings | Result |
|---|---|---|
| API docs draft sent to a contractor | Tiled diagonal, CONFIDENTIAL, opacity 40 | Every printed page shows the label |
| Pricing sheet for an internal review | Header stamp on pages 1-4 only | Cover pages marked, appendix left clean |
| Signed contract scan forwarded around | Centered stamp with the case number | Recipients see the file status at a glance |
| Course reader copied for a study group | Tiled diagonal, DRAFT, full range | Copies carry the stage of the work |
Common Mistakes
- Leaving the page box half filled by accident. A range such as 1-3 marks only those pages, and the rest of the document keeps no stamp at all.
- Dropping opacity to the bottom of the slider. Five percent reads on a bright screen and vanishes on a printed sheet; forty is a safer floor for text that must survive paper.
- Typing a full sentence into the text box. The tiled layout shrinks the font to fit the words, and a long line turns into a gray smear instead of a readable label.
- Treating the stamp as copy protection. These marks are ordinary text operators, and an editor that rewrites content streams can take them off again.
Best Practices
- Match the layout to the life of the file: tiled diagonal for drafts that get printed and passed around, centered for a single clear label, header for letterhead-style marking.
- Keep the stamp to one or two words. Short text holds a larger font at the same page coverage, and readers parse it faster.
- Mark a range when the document contains pages that should stay clean, such as a blank signature sheet at the end.
- Stamp first, then add page numbers with the numbering tool on the file that comes back, so both marks live in one document.
Frequently Asked Questions
Is this PDF watermark tool free?
Yes. The page runs in your browser with no account and no upload limit, and the output carries only the stamps you asked for. Nothing is added to the file by us beyond a producer label in the document properties.
Do my PDF files get uploaded?
No. The file is read into browser memory with the File API, pdf-lib draws the stamps, and the result becomes a local download link. Closing the tab discards everything, including the link.
What is the difference between tiled, centered, and header stamps?
Tiled diagonal repeats the text across the whole page at a 45 degree angle, which suits drafts that get printed and passed around. Centered draws one large faint stamp in the middle of the sheet. Header places a single line near the top edge, which works well on reports that keep a clean footer.
Which fonts and sizes are used for the watermark text?
Helvetica Bold is embedded into the PDF for every run, so the stamp renders the same on any machine. The size is worked out per page from the page width and the length of your text, and the opacity slider from 5 to 100 percent controls how dark the stamp prints.
What happens with a password-protected PDF?
pdf-lib cannot open an encrypted document, so the page reports that the PDF could not be opened and produces no output. Remove the password with a desktop tool first, then stamp the copy that opens without one.
Can recipients remove the watermark?
Treat this as labeling rather than protection. The stamps are ordinary text drawn with vector operators, so an editor that rewrites content streams can erase them. Use it to mark drafts and internal copies, not to stop determined copying.
Can I add page numbers in the same run?
Stamp the watermark first, then open the Page Numbers tool and run it on the file that comes back. Each tool writes a fresh document, so the stamps from the first pass are still there when the numbers land.