Watermark PDF, Stamps & Confidential Marks

About Watermark PDF, Stamps & Confidential Marks

There are three broad ways to put a “CONFIDENTIAL” mark or a logo on a PDF: attach it as an annotation, draw it into the page's content stream, or flatten the whole page into an image. Which one you pick decides how easily the recipient can take the mark off again.

All three tabs of this tool — Watermark, Stamp and Confidential mark — use the second approach. Text is added as real vector text and shapes as paths, alongside the untouched original content. It stays sharp at any zoom and barely grows the file, but it is not an unremovable watermark, and it's worth knowing why.

Annotation, content stream, flattened: from easiest to hardest to remove

An annotation is a separate object floating above the page. The PDF specification (ISO 32000-1, 12.5.6.22) even defines a dedicated Watermark annotation type. Annotations show up in a viewer's comments panel and can be deleted with a click, so this is the weakest option.

A watermark drawn into the content stream lives in the same layer as the body text. It doesn't appear in the comments list, so a casual reader can't just delete it, but any PDF editor that lets you select page objects can remove it. Because this tool writes real text, the watermark is also searchable and copyable: tile “CONFIDENTIAL” across a page and it may turn up between words when someone copies a paragraph.

Flattening renders the page to pixels, fusing watermark and content. It's the hardest to undo, but the text stops being searchable and the file gets bigger. If the goal is tracing a leak, a practical order is: tile the mark across the whole page so it can't be cropped out, and if that isn't enough, convert the result to an image-only PDF.

Over or under the content — and why it vanishes on scans

In the Watermark tab, choosing “under content” moves the new drawing stream in front of the original one. In a PDF, whatever is painted first ends up at the bottom, so the text sits on top of the watermark and stays easy to read.

The catch is scanned documents. Each page of a scan is one opaque photo, white background included, so a watermark placed underneath is completely hidden by it. Even PDFs exported from Word can hide parts of an underlay wherever a table cell or shape has a white fill. For scans, use “over content” at low opacity, around 20–35%. When you choose “under content”, the tool looks for pages where an opaque image (one without a transparency mask) covers at least 95% of the visible area and lists them on the result screen with a warning that the watermark is hidden there. Non-image covers such as white-filled shapes aren’t detected, so check the result.

Stamp tab: an approval stamp, drawn in vectors

The Stamp tab places words such as “APPROVED” or “DRAFT” inside a rectangle, rounded rectangle or circle. You set the width in millimetres (45 mm by default), an optional double border, one of four colours (red, blue, green, black) and a second line; typing {date} there inserts the chosen date as 2026.09.22. The text is sized automatically to fit the border, and the main line is limited to 40 characters.

A vector stamp is not a signature image and carries no legal weight on its own. It is a workflow marker that says which version was approved.

Confidential mark tab: an angle that follows the page

This tab writes a classification — CONFIDENTIAL, SECRET, TOP SECRET, INTERNAL USE ONLY, DO NOT COPY, or Korean grades such as 대외비 — in red along the page's bottom-left to top-right diagonal. The angle isn't fixed at 45°: it is computed from the page's own proportions, so US Letter portrait (612×792 pt) gets about 52.3° and A4 portrait about 54.8°. The text length is a share of the diagonal (30–95%, default 75%), and its height is capped at 32% of the short side so a short word doesn't balloon.

Optionally a solid grade label is added at the top and bottom centre, so the classification survives even if a copy is trimmed. Besides PDFs, this tab accepts Word, Excel and image files. Word gets a genuine Word watermark object; Excel has no watermark feature, so the mark goes in as a header picture, visible only in Page Layout view, print and PDF export.

Worked examples

How to use it

1. Pick a tab (Watermark, Stamp or Confidential mark) and open the file.
2. Set the text or image, size, opacity and position on the preview.
3. Choose the page range and save.

Frequently asked questions