Does watermarking increase the PDF file size?

Text watermarks add negligible size. Image watermarks embed the image once and reference it per page, so the increase is roughly the image file size — typically a few KB for a logo PNG.

Can I watermark a password-protected PDF?

No — encrypted PDFs must be unlocked first. Use the PDF Password tool to remove protection, then apply the watermark here.

Can the watermark be removed later?

Watermarks added by this tool are embedded directly into the page content stream, making them difficult to remove without specialised editing software. They are not annotation layers.

What's the best opacity for a subtle background watermark?

For a ghost watermark that is visible but does not obscure content, 15–25% works well. For a proof stamp intended to be clearly visible, use 50–70%.

Will the watermark print correctly?

Yes. The watermark is written into the PDF content stream at full print resolution — it will appear exactly as in the preview when printed.

PDF Watermark

Stamp a text or image watermark on every page — diagonal, center, or tiled placement.

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Draw, type, or upload a signature and click to place it on any PDF page.

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Drag pages to reorder, rotate individual pages, and delete pages — then export.

Compress PDF

Compress PDFs to a fraction of their size — perfect for email.

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Lock sensitive PDFs with a password or remove existing protection.

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How PDF Watermarking Works — Text, Images, and Layout Modes

PDF Watermark stamps a text label or image onto every page of a PDF using pdf-lib. The watermark is written directly into each page's content stream as native PDF objects — vector text for the text watermark, an embedded XObject image for picture watermarks. This makes it part of the document rather than a removable annotation layer. pdfjs-dist renders thumbnails so you can preview placement before exporting.

Text watermarks accept any string (CONFIDENTIAL, DRAFT, DO NOT COPY, an internal version label) and any hex color. Font size ranges from 18 pt to 120 pt. Three layout modes are available. Diagonal places the text rotated 45° centered on the page — the classic legal stamp look. Center renders it upright in the middle. Tile repeats the text across the whole page in a grid, useful for proof images where you want the watermark visible regardless of crop.

Image watermarks accept PNG and JPEG. PNGs with a transparent background are recommended so only the logo or stamp shows through; JPEGs always include a rectangular background. Scale is configurable as a percentage of page width, and opacity ranges from 0 (invisible) to 100 (fully opaque). 15–25 % is the typical choice for a subtle background watermark; 50–70 % for a clearly visible proof stamp.

Per-page positioning controls let you offset from any corner or use page-relative coordinates. The watermark applies to every page by default, but page selection lets you limit it to a range — for example, watermarking only the body pages of a report and leaving the cover untouched.

Because the watermark is embedded in the content stream, it cannot be removed by simply deleting an annotation layer. Specialized tools could edit the stream and strip it, but for the typical recipient using a standard PDF viewer it is permanent. Opacity is implemented via a Graphics State (gs) dictionary referencing CA/ca alpha values, which is honored by every modern PDF reader.

Encrypted PDFs cannot be parsed by pdf-lib until they are unlocked, so password-protected files must be cleared first using the PDF Password tool. Existing digital signatures are invalidated by adding a watermark because the page bytes change — this is part of the PDF signing standard.

Browser memory is the practical limit. PDFs up to about 200 MB and 1000 pages watermark comfortably on a modern laptop. Image watermarks embed the picture once and reference it from each page, so file size grows roughly by the size of the source image plus a small per-page reference cost — typically a few KB for a logo PNG.

Common Use Cases

Mark documents as CONFIDENTIAL

Stamp a diagonal CONFIDENTIAL or DRAFT watermark before sharing sensitive documents externally — the standard look for legal redlines and financial drafts.

Brand PDFs with your logo

Overlay a company logo at low opacity on reports, proposals, and presentations to reinforce brand identity without obscuring content.

Discourage unauthorized copying

Tile a semi-transparent copyright or DO NOT COPY watermark across every page so screenshots and re-shares carry the mark.

Identify recipients on shared PDFs

Stamp the recipient's name across each copy so leaks can be traced back to the original audience member.

Frequently Asked Questions

Text watermarks add negligible bytes — a few hundred per page for the embedded font subset and content stream additions. Image watermarks embed the image once and reference it from every page, so the increase is roughly the source image size plus a small per-page reference (typically a few KB for a logo PNG).

Not easily. Because the watermark is written into each page's content stream as native PDF objects, it isn't a simple annotation layer that a viewer can hide or delete. Removing it requires editing the content stream with specialized tools like qpdf or Adobe Acrobat Pro.

15–25 % for a watermark that is visible but doesn't obscure content. 50–70 % for a proof stamp intended to be clearly visible. 100 % for an opaque overlay that fully covers the underlying area.

PNG and JPEG. PNGs with a transparent background are recommended for logos and stamps so only the artwork shows through; JPEG always includes a rectangular background. SVG support varies by version of pdf-lib used.

Not directly — pdf-lib refuses to parse encrypted streams. Remove the password using the PDF Password tool first, watermark, then re-encrypt if needed.

Yes. The watermark is part of the page's content stream and prints at full resolution — it appears exactly as it does on screen. The Graphics State alpha values are honored by every modern print driver.

Yes. Page selection accepts ranges and specific pages, e.g., 3-50 to skip the cover and back matter. Different watermarks per page require multiple passes.

Yes. Any modification to a signed PDF — including watermarking — invalidates existing digital signatures. This is part of the PDF signing standard and applies to every PDF tool, including Acrobat.

No. pdf-lib writes the watermark and pdfjs-dist renders previews, both inside your browser. The PDF stays in tab memory and is never transmitted.

It depends on the watermark color and opacity. White text at 30 % opacity is usually visible on dark backgrounds; black text at the same opacity disappears. Test on a representative page before applying to a long document.

Step-by-step guide

How to add a watermark to a PDF

Walk through every step with screenshots, format-specific tips, and the platform-by-platform limits you need to know.