A watermark tells the reader what a document is before they read a word of it — a draft that should not be quoted, a copy that is not the original, or a file that was shared in confidence. This stamps text diagonally across the pages you choose.
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Result
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What the Add Watermark to PDF does
The text is drawn onto each page at the opacity and angle you set, centred and rotated. It sits on top of the existing content, which is untouched underneath — remove the watermark by working from your original file, not by editing the stamped one.
Opacity is the setting that matters. Too faint and it does not register; too strong and the document becomes hard to read. Between 10% and 20% is the range that works for almost every document.
How to use this tool
- Select your PDF and wait for the thumbnails.
- Type the watermark text. Short words such as DRAFT, COPY or CONFIDENTIAL work best.
- Set the opacity — start at 15% and adjust if it is too faint or too heavy.
- Tick specific pages if only some need marking, or leave all unticked for the whole document.
- Press Add watermark and download.
How the watermark is placed
The text is measured, then centred and rotated:
text width = font.widthOfTextAtSize(text, size)
x = page width ÷ 2 − (text width ÷ 2) × cos(angle)
y = page height ÷ 2 − (text width ÷ 2) × sin(angle)
Drawn with the chosen opacity and rotation on top of the
existing page content, which is not modified.
A watermark is a visual mark, not protection — it can be
removed by re-rendering the page.
Worked example
Example: circulating a draft
| Text | DRAFT — NOT FOR CIRCULATION |
| Size | 36 pt (long text needs a smaller size) |
| Opacity | 12% |
| Angle | 45° |
Long watermark text at 60 pt runs off the page. Reduce the size as the text gets longer.
What your result means
The document stays fully readable at sensible opacity — that is the point of a watermark rather than a stamp.
It is not security. Anyone can strip a watermark by converting pages to images and back, or by cropping. It signals intent; it does not enforce it.
Your original is untouched, so keep it as the clean master copy.
Important considerations
- Reduce the font size as text gets longer. A 60 pt watermark only suits a single short word.
- Grey is the least intrusive; red reads as a warning and suits CONFIDENTIAL or DRAFT.
- Watermarking after merging is usually right — otherwise only some sections carry the mark.
- For content that must not be readable at all, use redaction instead.
- Adding a watermark invalidates any digital signature on the document.
Limitations of this tool
- Password-protected PDFs cannot be opened without the password.
- Processing happens in your device's memory, so very large documents can be slow.
- Existing text cannot be edited or removed — these tools add content on top of the page.
- Text watermarks only — image watermarks and logos are not supported. Use Add Image to PDF for a logo.
- Only the standard PDF fonts are available, so Devanagari and other Indic scripts cannot be used.
- A watermark can be removed by anyone; it offers no protection.
Frequently asked questions
What opacity should I use for a watermark?
Between 10% and 20%. Below 8% it is barely visible; above 30% it starts to interfere with reading the document.
Can I use my logo as a watermark?
Not with this tool, which places text. Use Add Image to PDF to position a logo on the page.
Does a watermark protect my document?
No. It is a visual mark that can be removed by re-rendering or cropping the pages. It communicates status; it does not enforce anything.
Why does my watermark run off the page?
The text is too long for the font size. Reduce the size — long phrases usually need 30–36 pt rather than the 60 pt default.