Fix Watermark renedering issue in Generated PDFs

The watermark in generated PDFs is currently inconsistent.
Examples of issues:
1. Only appears on the first page
2. Misaligned / overlapping
3. Low resolution or blurred
4. Missing on multiple pages

The goal is to ensure correct placement, opacity, quality, and multi-page support.

Steps to Reproduce
1. Go to PDF Converter section after generate email
2. Download the pdf of generated email
3. Check the watermark

Expected Behavior
1. Watermark appears on every page, in a consistent position
2. Correct opacity (20–30%), no blur
3. Works with portrait + landscape
4. Correct scaling on all devices
5. No clipping or overlap with content

Problematic file:
-email-pdf.js

If you’re interested, just comment ‘assign me’ — I’ll assign it quickly.

Problem sample:

Start with email-pdf.js and reproduce the issue by generating an email PDF from the PDF Converter section, then inspect the watermark across portrait and landscape pages. Done means the watermark appears on every page with consistent placement, 20–30% opacity, clear quality, correct scaling, and no clipping or overlap.

Written by the indexing model from the issue text.