select the text, and then add a bookmark... it will now be highlighted in yellow
sorry but that's all i think DE can do. it's a piece of **** software.
You have to remember that Digital Editions was never designed to have 'text
editor' capabilities. BTW: Bluefire and Overdrive also have such
limitations. Put in another frame of reference, DE presents you with the
ebook, as you would be presented with a physical printed book.