Watermarking of downloadable files

The watermarking module automatically adds buyer details to downloadable files (PDF and EPUB) at the moment of download. Each downloaded file contains a personalized watermark identifying the buyer.

Requirements

Polski PRO requires: Polski (free) v1.5.0+, WordPress 6.4+, WooCommerce 8.0+, PHP 8.1+. The PHP ZipArchive extension is required for EPUB files.

How it works

1. The customer buys a product with downloadable files
2. At the moment the download link is clicked, the plugin intercepts the request
3. Depending on the file format, the appropriate watermarking mechanism is applied
4. A temporary watermarked file is generated and sent to the customer
5. The temporary file is removed once the process completes (cleanup on shutdown)

Watermarking is applied automatically to all products with downloadable files, no additional per-product configuration is required.

Supported formats

PDF (TCPDF)

Watermarking of PDF files uses the TCPDF library:

• The watermark text is overlaid on every page of the document
• The text is semi-transparent and placed diagonally across the page
• The watermark does not affect the readability of the original content
• Multi-page PDF documents are supported

EPUB (ZipArchive)

Watermarking of EPUB files uses the PHP ZipArchive extension:

• The EPUB file is opened as a ZIP archive
• A <div> element with the buyer’s details is injected into the HTML files inside the archive
• The injection happens before the closing </body> tag
• The original EPUB structure is preserved

Placeholders

You can use the following placeholders in the watermark content:

Placeholder	Description	Example
[FIRSTNAME]	Buyer’s first name	Jan
[LASTNAME]	Buyer’s last name	Kowalski
[EMAIL]	Buyer’s email address	[email protected]
[DATE]	Date the file was downloaded	2026-04-06
[ORDER_ID]	Order number	12345

Example watermark text:

Licensed to: [FIRSTNAME] [LASTNAME] ([EMAIL])
Order #[ORDER_ID] from [DATE]

Temporary files

The watermarked file is created as a temporary copy in the wp-content/uploads/polski-pro-temp/ directory:

• The temporary file is generated with a unique identifier
• After the file is sent to the customer, the temporary file is removed
• Cleanup happens automatically via the register_shutdown_function hook
• In case of an error, the temporary files are also removed

Configuration

Go to WooCommerce > Settings > Polski PRO > Watermarking.

Setting	Description
Enable watermarking	Activates the module for all downloadable files
Watermark text	Watermark content with placeholders
Font size (PDF)	Size of the watermark text in the PDF
Transparency (PDF)	Transparency level of the watermark in the PDF
CSS style (EPUB)	CSS style of the watermark div element in the EPUB

Enabling the module

The module is controlled by a toggle in the PRO module settings:

WooCommerce > Settings > Polski PRO > Modules > Watermarking

This page is for informational purposes only and does not constitute legal advice. Polski PRO for WooCommerce is commercial software provided without warranty.