Use a watermark as a signal, not a disguise
A watermark is most helpful when it communicates status: DRAFT, CONFIDENTIAL, SAMPLE, PAID, or an organisation name. It should be clear enough to survive a screenshot without making the actual page unpleasant to read. The live preview lets you balance colour, opacity, size, and placement on a real page rather than relying on a generic setting.
A large diagonal mark works for a simple status label. A small straight mark in a corner suits internal documents that still need to be readable. A tiled pattern is stronger for samples that may be shared widely. Select the exact pages to mark; a cover or an appendix sometimes needs a different treatment from the body of a document.

