Watermark PDF

Between 10% and 20% for a background mark — visible enough to be unmistakable, faint enough that the text underneath stays readable. Go higher only when the point is to obstruct rather than to label, such as marking a specimen document that must not be usable.

One centred mark is cleaner and is enough for internal labelling. Tiling covers the whole page and is much harder to crop out, so it is the better choice for anything you are worried about being screenshotted or trimmed.

Yes — by anyone determined. It is drawn as text in the page content, so a PDF editor can delete it, and rasterising plus inpainting defeats even a flattened one. A watermark is a deterrent and a label, not a security control. If a document must not be altered, protect and flatten it as well.

Yes. The watermark is drawn on top of whatever the page contains, image or text, so scans mark the same way. It will not be searchable text over a scan, but neither is the scan.

Yes — enter the pages as "1, 3-5". Blank means every page. A common pattern is marking only the pages carrying pricing or personal data rather than the whole document.

The tool uses the standard PDF fonts, which cover Latin scripts only. Non-Latin characters have no glyphs there and would be dropped, so the tool asks for Latin text instead of silently producing a blank mark.

No. It is opened, stamped and saved entirely in your browser. Documents worth watermarking are usually the ones you least want on someone else's server.

Not with this tool — it stamps text. To lay a logo or letterhead over every page, use PDF Overlay, which stamps a second PDF onto each page and takes an opacity setting.