add diagonal watermark to pdf

A diagonal angle works well for watermark text because it reads clearly at a glance without directly overlapping the horizontal flow of body text on the page. An angle in the 30 to 45 degree range is the most common choice, striking a balance between being noticeable and not obscuring the document's actual content.

The steeper the angle, closer to 90 degrees, the more the watermark starts to look like a vertical side stamp rather than a diagonal one, which can work for narrow labels but reads less naturally for longer phrases like 'CONFIDENTIAL DRAFT COPY.' A shallower angle, closer to 0 degrees, starts to look like ordinary horizontal text rather than a distinct diagonal watermark.

Combine the angle with font size and opacity thoughtfully: a large, bold diagonal watermark at high opacity commands attention immediately, which suits genuinely sensitive documents. A smaller, lighter diagonal watermark at lower opacity provides a subtler status indicator without overwhelming the page, which works well for internal drafts where the emphasis should stay on the content.

Preview the result across a few different pages of your document before downloading, especially pages with different amounts of text or images, since a watermark angle that looks perfect on a mostly-empty page can look different crossing a page full of dense text or a large image.