FO2PDF is a native-mode XSL FO processor: the whole procedure of calculating the layout of every page is performed inside, without recurring to any third-party formatting engine - nroff, TeX or whatever else. Such an approach is sometimes more difficult to implement: e.g. coding an algorithm for footnotes placement on a multi-column page has never been easy. On the other hand, native mode processing gives you considerable advantages in flexibility and cross-
FO2PDF builds an exact internal representation of page layouts and then outputs it to the desired media using only the simplest graphic primitives. Therefore, it is relatively easy to add more output formats to the system. Current output formats include PDF and PostScript (experimental); PCL version is envisaged.
In its current shape, FO2PDF supports a fairly representative subset of XSL Formatting Objects. Within this subset, it is already possible to write complex styles for producing fine-looking documents.
OK, so you want to stamp your document. Maybe you need to give reviewers some advice about the document's status or sensitivity. This tip from author Ted Padova demonstrates how to add stamps with the Stamp Tool along with related comments.