When prince is used in "free" mode, it adds a non-printing watermark in the upper-right corner that appears when you open the PDF in an electronic viewer program but disappears when the doc is printed.

I would also like to add some elements that are visible only in the electronic copy of the PDF, but not in the physical printout.

I couldn't find any selectors to indicate this. Am I missing something?

-c

We don't yet support a CSS mechanism to create arbitrary PDF annotations, although we hope to add one in the future.

The latest builds now support PDF text annotations!