How to add a confidential watermark to a pdf document
- Step 1Open the watermark tool and drop in the PDF — Load the document into pdf-watermark. One PDF at a time — the tool processes a single file per run, not a batch.
- Step 2Set the watermark text to CONFIDENTIAL — The text field defaults to
CONFIDENTIAL. Leave it, or type a fuller phrase such asCONFIDENTIAL — INTERNALorCONFIDENTIAL — Project Atlas. Longer text is auto-scaled down to fit the page width. - Step 3Choose an opacity — Opacity accepts 0.05–1.0 in 0.05 steps; the default is 0.15. For a confidential marking that's visible but doesn't fight the body text, 0.15–0.25 is the practical range. Lower (0.05–0.10) is barely-there; higher (0.30+) starts to dominate.
- Step 4Set the font size — Font size accepts 12–200 pt; the default is 60. The number you enter is a starting size — the tool scales it relative to the page diagonal and then shrinks further if the text would overflow, so 60 on a standard A4/Letter page gives a large central watermark.
- Step 5Apply the watermark — Run the tool. It opens the PDF, embeds bold Helvetica once, and draws the centred diagonal text on every page. There is no page-range selector — the marking is uniform across the document by design.
- Step 6Download and check the result — The result panel reports the page count of the output. Download the watermarked PDF and distribute that copy only — keep the original un-watermarked file for your own archive. To layer access control on top, follow with pdf-permission-setter.
What you can and can't control
The real UI exposes exactly three inputs. Everything else is fixed by design. Verified against the tool implementation.
| Property | Control | Range / value | Notes |
|---|---|---|---|
| Watermark text | Text input | Any string (default CONFIDENTIAL) | Empty text falls back to CONFIDENTIAL; long text auto-shrinks to fit |
| Opacity | Number input | 0.05 – 1.0, step 0.05 (default 0.15) | 0.15–0.25 is the legible-but-unobtrusive range for confidential marking |
| Font size | Number input | 12 – 200 pt (default 60) | A starting size — scaled to the page, then shrunk if it would overflow |
| Colour | None (fixed) | Mid-grey | No colour picker or hex input — the watermark is always mid-grey |
| Rotation | None (fixed) | -45° diagonal | Always diagonal, bottom-left to top-right, centred on the page |
| Pages affected | None (fixed) | All pages | No page-range option; every page gets the same watermark |
| Font | None (fixed) | Helvetica Bold | Standard font, embedded once for the whole document |
Confidential-marking opacity guide
Opacity is the lever you'll actually tune. These are practical starting points for confidential documents at the default font size.
| Opacity | Appearance | Best for |
|---|---|---|
| 0.05 – 0.10 | Very faint, ghost-like | Documents that must stay highly readable on screen; a subtle deterrent |
| 0.15 (default) | Clearly present, body text fully legible | Most internal confidential reports and decks |
| 0.20 – 0.25 | Prominent | NDA disclosures where the marking should be the first thing noticed |
| 0.30 – 0.50 | Dominant, starts to compete with content | Single-page cover sheets or summaries, not full reports |
| 0.60 – 1.0 | Heavy / near-solid grey | Rarely useful — obscures the underlying text |
Tier limits for the input PDF
Watermarking processes one file per run. Limits are by file size and page count. Real values from the tier configuration.
| Tier | Max file size | Max pages | Files per run |
|---|---|---|---|
| Free | 2 MB | 50 | 1 |
| Pro | 50 MB | 500 | 1 (watermark is single-file) |
| Pro + Media | 500 MB | 2,000 | 1 |
| Developer | 2 GB | 10,000 | 1 |
| Enterprise | Unlimited | Unlimited | 1 |
Cookbook
Concrete confidential-marking setups. Each shows the three inputs you set and what the tool produces.
Standard internal CONFIDENTIAL marking
The default-driven case: a multi-page internal report you want clearly marked but still comfortable to read.
text: CONFIDENTIAL opacity: 0.15 fontSize: 60 → mid-grey 'CONFIDENTIAL' drawn diagonally at -45°, centred on every page, body text fully legible.
NDA disclosure that should be impossible to miss
For documents shared under a signed NDA, push opacity up so the marking is the first thing a recipient registers.
text: CONFIDENTIAL — NDA opacity: 0.25 fontSize: 60 → prominent diagonal marking. The longer text auto-scales to stay inside the page margins.
Project-scoped confidential label
Tie the marking to a code name so a leaked page is attributable to a workstream without naming individuals.
text: CONFIDENTIAL · PROJECT ATLAS opacity: 0.18 fontSize: 54 → the phrase is long, so the tool shrinks the font below 54 to fit ~72% of the page diagonal — still centred, still diagonal.
Subtle on-screen deterrent
When the document is read mostly on screen and you want a marking that's present but never in the way.
text: CONFIDENTIAL opacity: 0.08 fontSize: 60 → faint ghost watermark. Visible on inspection, invisible to a casual skim — a light-touch handling signal.
Mark first, then lock down permissions
A watermark is a visual signal, not access control. Chain it with the permission setter for the actual restriction.
Step 1 — pdf-watermark: text: CONFIDENTIAL opacity: 0.20 fontSize: 60 Step 2 — pdf-permission-setter: set an owner password, disable copy + print → document is both visibly marked and technically restricted.
Edge cases and what actually happens
You want the watermark in red instead of grey
Not supportedThere is no colour control — the watermark is always rendered in mid-grey. If brand or alert colour is essential, build a single-page coloured watermark graphic and overlay it with pdf-stamp, which composites any single-page PDF over every page.
You only want the cover page (or a page range) marked
Not supportedThe watermark is applied to every page; there is no page-range selector. To mark only specific pages, extract them with pdf-extract-pages, watermark that subset, then merge it back with pdf-merge.
Your CONFIDENTIAL phrase is very long
PreservedLong text doesn't overflow — the tool measures the string and caps its width at roughly 72% of the page diagonal, shrinking the font as needed (down to a 16 pt floor). A phrase like CONFIDENTIAL — DO NOT FORWARD OR PRINT renders smaller but stays centred and on-page.
The PDF is password-protected
SupportedThe tool loads the document with encryption ignored, so it can read and watermark a restricted PDF in many cases. Note the output is saved un-encrypted; if you need the result to stay protected, re-apply protection with pdf-permission-setter or pdf-password-protect afterwards.
Pages are mixed sizes or orientations
ExpectedEach page is measured independently — the watermark is scaled to that page's diagonal and centred on it. A document mixing A4 portrait and A3 landscape pages gets a correctly-sized diagonal marking on each, not a single fixed-size stamp.
The recipient deletes the watermark
By designThe watermark is drawn into the page content, not a removable layer — but it is not encryption. A determined user with PDF-editing software can remove drawn content. Treat the marking as a strong deterrent and clear statement of intent, and pair it with pdf-permission-setter for actual restriction.
Free-tier file over 2 MB or over 50 pages
RejectedFree tier caps the input at 2 MB and 50 pages. A larger confidential report needs Pro (50 MB / 500 pages) or higher. If the file is large only because of images, run it through pdf-compress-lossy first, then watermark.
You re-watermark an already-watermarked PDF
ExpectedRunning the tool again adds a second diagonal marking on top of the first — they stack. To change the text or opacity, re-watermark the original clean file rather than the already-marked one, or you'll end up with overlapping text.
Page content already fills the centre with dark imagery
Reduce opacityA low-opacity grey watermark can be hard to read over a dark full-bleed image. Raise the opacity toward 0.25–0.30 so the marking reads against the imagery, accepting that it's more prominent over lighter pages.
You need a per-recipient identifier for leak tracing
Use the text fieldPut the recipient or copy ID directly in the watermark text — e.g. CONFIDENTIAL — Copy 014 — and run the tool once per recipient. There's no automated mail-merge, but a distinct text string per export gives you a traceable marking.
Frequently asked questions
Can recipients remove the CONFIDENTIAL watermark?
The watermark text is drawn into the page content rather than stored as a separate removable layer, so it survives normal viewing, printing, and copying of the file. It is not encryption, though — someone with capable PDF-editing software can remove drawn content. Treat it as a strong visual deterrent and statement of handling intent. For an actual restriction, follow up with pdf-permission-setter.
What opacity works best for a CONFIDENTIAL marking?
0.15 (the default) to 0.25 is the practical range. The opacity field accepts 0.05–1.0 in 0.05 steps. Below 0.10 the watermark is a faint ghost; above 0.30 it starts to compete with the body text. For most internal reports, leave it at 0.15; for NDA disclosures where the marking must be unmissable, use 0.20–0.25.
Can I use my company brand colour for the watermark?
No — the watermark colour is fixed mid-grey; there is no colour picker or hex field. If a specific colour is essential, create a one-page coloured watermark graphic (in any design tool, exported to PDF) and overlay it on every page with pdf-stamp instead.
Can I watermark only the body pages and leave the cover clean?
Not directly — the watermark applies to every page and there is no page-range control. The workaround is to split the document with pdf-extract-pages, watermark only the body subset, then reassemble with pdf-merge.
Will a long phrase like 'CONFIDENTIAL — DO NOT DISTRIBUTE' fit?
Yes. The tool measures your text and, if it would be too wide, shrinks the font (down to a 16 pt minimum) so the watermark spans about 72% of the page diagonal and stays centred. Longer phrases simply render at a smaller size rather than running off the page.
Does the watermark go on the front or behind the page content?
It's drawn on top of the existing page content at the opacity you choose, so at low opacity the body text shows clearly through the semi-transparent grey marking. There's no option to push it strictly behind the content, but at 0.15–0.25 opacity the visual effect is that of a background watermark.
Can I watermark several PDFs at once?
The watermark tool processes one PDF per run — it isn't a batch tool. Run each file individually. If you regularly mark many documents, the pattern is to script it: the tool runs the same operation locally each time you load a file.
Is my confidential document uploaded anywhere?
No. The watermarking happens entirely in your browser — the PDF is loaded, marked, and saved on your device, and the file content never reaches a server. That local-only processing is the main reason this tool suits documents you're marking confidential in the first place.
What font and angle is the watermark?
Bold Helvetica, drawn diagonally at -45° (bottom-left to top-right) and centred on each page. Both are fixed — there's no font picker or angle control. The fixed diagonal layout is what gives every page a consistent, recognisable confidential marking.
Can I add a logo as the watermark instead of text?
This tool is text-only. For an image or logo watermark, use pdf-stamp, which overlays the first page of a stamp PDF (which can be a logo) onto every page of the base document.
What's the largest confidential PDF I can watermark?
It depends on your tier: 2 MB / 50 pages on Free, 50 MB / 500 pages on Pro, 500 MB / 2,000 pages on Pro + Media, and 2 GB / 10,000 pages on Developer. Enterprise is unlimited. If a file is over the limit mainly because of images, compress it first with pdf-compress-lossy.
Should I keep an un-watermarked original?
Yes. The watermark becomes part of the page content of the output, and there's no built-in 'remove watermark' step. Always keep the clean source PDF so you can produce a final un-marked version later, or re-watermark with different settings without stacking markings.
Privacy first
All PDF processing runs locally in your browser using PDF-lib and pdf.js. No file is ever uploaded — only metadata counters are saved for signed-in dashboard stats.