Before you begin, make sure the sections of your document are properly formed out with consistent Title styles, font, margins, and page numbers. This will help ensure the watermark you add will appear only on pages with the Title style you specify.

1. Create a watermark image and save the PDF file.
2. In the 'Page Layout' tab choose 'Watermark' and select 'Custom Watermark'.
3. In the 'Page Range' field choose 'Pages with this Title' and select the Title style you want the watermark to appear on.
4. Browse for your watermark image and click 'Insert'.
5. Select 'Behind Text' then hit 'OK'.
6. Save the document to apply the changes.