File → Headers & footers… stamps running text onto every page. On the Header/Footer tab, choose a header or a footer, its alignment, the text and its size. Use {page}, {total} and {date} and Seben fills them in, so Page {page} of {total} becomes “Page 3 of 12”.
The Watermark tab places semi-transparent text across the middle of each page, with the size, opacity and angle you choose.
The Bates tab, also reached from File → Bates numbering…, applies sequential numbering with a prefix, a starting number and a number of digits, at the left, center or right of the page. It is the stamping used for discovery and case files, where every page needs its own reference.
A preview shows how the first page will read before you apply anything. Stamped text supports Western European characters.
Every stamp is a new version, so you can undo it from File → Version history like any other change.