PDF Watermark & Numbers
Stamp custom text watermarks, confidential overlays, and page numbers onto PDF documents in browser.
Drag & Drop PDF file to add watermark
Upload single PDF up to 100MB. 100% Private local processing.
Text Watermark Settings
Live Stamp Preview
How do I use PDF Watermark & Numbers?
Upload your PDF document or click "Load Sample Data" to load a sample corporate PDF.
Customize watermark text (e.g., `CONFIDENTIAL`, `DRAFT`), font size, rotation angle (`-45°`), color, and opacity.
Preview the live watermark overlay and click "Apply & Download PDF" to save the stamped file.
What features does PDF Watermark & Numbers offer?
Precision vector text stamping: Custom typography, colors, font sizes, and rotation angles
Granular opacity & alpha blending control (10% subtle background to 100% solid foreground overlay)
Automated dynamic 'Page X of Y' pagination for bottom-center, bottom-right, or top-right margins
Lossless stream injection: Preserves original vector text clarity, bookmarks, and internal hyperlinks
Interactive live parameter configuration with instant visual layout feedback
100% private in-browser client execution powered by pdf-lib — zero server uploads
PDF Graphics State (`ExtGState`) & Affine Transformation Matrix (`cm`)
Watermarks are injected into each page's content stream using a 2D affine transformation matrix $[\cos\theta, \sin\theta, -\sin\theta, \cos\theta, t_x, t_y]$ and alpha graphics state.
| Watermark Parameter | PDF Stream Operator / Key | Recommended Value | Security & Visual Behavior |
|---|---|---|---|
| Opacity (Alpha) | /ExtGState << /ca 0.25 /CA 0.25 >> | 0.15 – 0.30 (15%–30%) | Keeps underlying body text 100% legible |
| Rotation Angle | cm / Tm [cos θ sin θ -sin θ cos θ x y] | -45° (Diagonal SW → NE) | Spans full page diagonal across multiple paragraphs |
| Layer Order (Z-Index) | Prepended vs Appended Content Stream | Over Content (Appended) | Visible over opaque scanned image pages |
| Font Embedding | Standard 14 Type1 (Helvetica-Bold) | 48pt – 72pt bold | Zero font file bloat (built into every PDF viewer) |
Frequently Asked Questions about PDF Watermark & Numbers
Why does a watermark placed "Under Content" disappear on scanned PDFs?
Scanned PDFs consist of a full-page opaque raster image (`/XObject`) covering 100% of the canvas. Always place watermarks **Over Content** with semi-transparent opacity (`0.20–0.30`) so they remain visible over scanned pages.
Does adding a text watermark increase the PDF file size significantly?
No. Because the watermark uses standard PDF built-in fonts (`Helvetica-Bold`) and a lightweight vector text operator stream (`BT ... ET`) of less than 200 bytes per page, file size increase is negligible (`< 5 KB`).
Can a vector PDF watermark be removed by someone with a PDF editor?
Vector text watermarks are added as distinct content stream operators, which deters casual copying and printing. For high-security uneditable watermarks, compress or rasterize the watermarked PDF afterward to flatten all layers.
How does the watermark stay centered across mixed Portrait and Landscape pages?
The engine reads each individual page's `getSize()` (`width` and `height` from `/MediaBox`) and dynamically computes the exact geometric center $(W/2, H/2)$ before applying the rotation matrix.
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