Watermark PDF Online Free – Private, In Your Browser
Stamp confidential, draft, or copyright notices onto any PDF without uploading it. Choose text or a PNG/JPEG logo, set opacity, rotation, and position, and apply the watermark to every page or a selected range. All processing runs inside your browser tab, and the watermarked file downloads straight to your device.
Drop your PDF here to watermark
Click to browse, drag and drop, or paste from clipboard
Select any PDF document. Add confidential, draft, or logo watermarks. Processed entirely in your browser.
Larger selections show a memory caution you can skip. Our measured laptop runs completed up to 100 MB for tools like this; phone browsers warn earlier.
Document Name
0 KB • 0 pages
Watermark Type
Live Page Preview
Network requests reported while processing: 0
Counted during an automated browser test that processed a real file, excluding the page's own HTML, CSS, and script downloads. Saved in docs/test-results/watermark-pdf.json.
How to use Watermark PDF
- 1 Drop a PDF into the workspace. The first page appears in the live preview, and the page selector lists every page in the document.
- 2 Choose Text or Image / Logo. For text, enter the wording and pick Helvetica, Times Roman, or Courier, a font size from 12 to 144, and a colour.
- 3 Set the position (diagonal centre, centre, or one of six edges), rotation (auto diagonal, 0°, 45°, −45°, or 90°), and opacity from 5% to 100%. Edge positions keep a 40-point margin.
- 4 Limit the stamp to a page range such as all, odd, even, 1-3, or 5. Page numbers outside the document are ignored.
- 5 Click Apply Watermark & Download PDF. The finished file downloads, and the result row reports its size and the number of pages stamped.
What it does — and what it doesn't
This tool parses the PDF object structure with @cantoo/pdf-lib inside your browser tab and adds a new text or image object to the content stream of each selected page. Text uses the standard Type 1 fonts built into the PDF format, while logos are embedded as PNG or JPEG image objects. The live preview rasterises pages with pdfjs-dist and overlays the watermark on a canvas at preview scale, so the saved file is produced from the PDF objects rather than from that canvas. Saving serialises the modified document in memory and hands the bytes to a Blob download. No document, logo, or watermark text is sent to a server.
Limits and browser boundaries
- Visual watermark only: the stamp is a normal PDF object, so it can be moved, covered, or removed later with a PDF editor. It is not encryption, DRM, or a tamper-proof seal.
- Fonts: standard Type 1 Helvetica, Times Roman, and Courier only. Custom font upload is not supported.
- Logos: PNG or JPEG images scaled from 10% to 100% of their natural size; transparency in PNG files is preserved.
- Encrypted PDFs: password-protected documents must be decrypted before a watermark can be applied.
- Memory caution: PDFs above 100 MB show a warning you can skip, the largest PDF a measured laptop run completed in this tool class (100 MB); phone browsers warn earlier. No hard size cap.
Measured on our test files
Real numbers recorded in automated browser tests, saved in docs/test-results/watermark-pdf.json.
| Fixture / Scenario | Input | Output / Result | Duration |
|---|---|---|---|
| sample-doc1.pdf600x400 pt · 1 pages | 679 B | 1.3 KB | 753 ms |
| sample-multipage.pdf600x400 pt · 4 pages | 981 B | 2.8 KB | 254 ms |
| large-doc-50mb.pdf600x400 pt · 25 pages | 50 MB | 50 MB | 878 ms |
| sample-multipage.pdf600x400 pt · 4 pages | 981 B | 126.3 KB | 372 ms |
Client-Side Privacy Proof
All computation executes strictly inside your device CPU and GPU memory. Your file bytes, photos, and document text are never uploaded or transmitted to any server.
Verify it yourself in 5 seconds:
- Press F12 (or right click → Inspect) and switch to the Network tab.
- Drop your file into the tool above and click process.
- Confirm that zero outbound requests or file payloads leave your computer.
Frequently asked questions
Are my PDF files or watermark images uploaded to any server?
No. PDF parsing, page preview, watermark placement, and file assembly all run inside your browser tab. No document bytes, logo data, or watermark text are transmitted. You can confirm this by opening the Developer Tools Network tab (F12) and watching that no upload occurs while the file is processed.
What did the measured lab runs show?
On 2026-10-27 our Playwright lab on a win32 x64 machine (Chromium 133.0.6943.16, 13th Gen Intel Core i3-1305U, 8 GB RAM) stamped CONFIDENTIAL across a 679-byte single-page PDF in 753 ms (1,342-byte output), a 981-byte four-page PDF in 254 ms (2,906-byte output), and a 52,440,216-byte 25-page PDF in 878 ms (52,449,514-byte output). A 1200×800 PNG logo at 30% scale on the four-page PDF took 372 ms and produced a 129,318-byte file. Timings include applying the watermark and starting the download. Full measurements are saved in docs/test-results/watermark-pdf.json.
Can I watermark only some pages?
Yes. Enter all, odd, even, or a list such as 1-3, 5 in the Target Pages field. Page numbers are one-based, and entries outside the document are ignored. If no page matches, the tool stops with a clear message instead of producing an empty result.
Does it work on scanned PDFs?
Yes. The watermark is added as a new PDF object on top of the existing page content, so it appears over scanned images and text alike. The tool does not read or change the scanned page content itself, and it does not perform OCR.
Can I use my company logo as the watermark?
Yes. Switch to Image / Logo, choose a PNG or JPEG file, and set the scale between 10% and 100% of the image's natural size. PNG transparency is preserved, which suits logos placed over page content.
Is the watermark permanent or legally protective?
It is a visual notice, not a security control. Anyone with a PDF editor can move, cover, or remove the stamp, and the file is not encrypted. For access control or tamper evidence, use document permissions or a digital signature instead.
Can I watermark a password-protected PDF?
No. The document must be opened and decrypted first; encrypted files are rejected with a message asking you to remove password protection before stamping.
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