Stamp a text watermark across all PDF pages.
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A determined person could re-extract the original page images and rebuild the file. A text watermark is a deterrent, not encryption. For real protection, combine with the Protect PDF tool to lock copying and editing.
Diagonal centre is harder to crop out than a bottom-corner label, so it is the standard for CONFIDENTIAL-style warnings. Horizontal looks cleaner for subtle branding.
This tool handles text watermarks. For a logo stamp, use the PDF + Image tool to place a PNG on each page.
Yes. Because it is drawn directly on the page content stream, it prints exactly as it appears on screen, at the opacity you chose.
Privacy: Watermarking is a local operation. Your PDF is never uploaded — the stamped file is built with pdf-lib inside this browser tab.