Why the original content is never actually touched#
A watermark is drawn as a fresh layer of text placed on top of each page, positioned and rotated independently of whatever content already exists there — nothing about the original text, images, or layout is modified, moved, or merged with the stamp. This is why a watermark works reliably regardless of what the underlying page contains: it does not need to understand or interact with that content at all, just draw on top of it.
Why opacity matters more here than in most drawing tools#
A watermark meant to mark a document as a draft or confidential copy needs to stay legible without obscuring the actual content underneath it — a solid, fully opaque stamp defeats the point by making the page hard to read. The default here sits at low opacity for exactly that reason; pushing it toward fully opaque is really meant for cases where obscuring the content partially is the actual goal, like a visible "SAMPLE" stamp on a preview document.
Why the text position is centered by measuring its actual width#
Centering text by eye or by a fixed offset looks wrong the moment the watermark text is longer or shorter than expected — "DRAFT" and "CONFIDENTIAL — INTERNAL USE ONLY" need very different horizontal offsets to land in the same visual center. This tool measures the actual rendered width of the watermark text in the chosen font and size before positioning it, so the centering adjusts automatically to whatever text is typed, rather than assuming a fixed length.