Unable to increase font size in epub file

When using Digital Editions to read an epub file, I am unable to increase/decrease the text size. I am able to enlarge the titles (via "EPUB Text Size" in the "reading"menu), but this does not manipulate the body text. The "PDF View" in the same reading menu seems to have options for zooming in/out on the text, but all of these options are greyed out. I have the most recent version - 4.5.11.