Yes you can catch a bus from Zadar to Plitvice, there are several lines that pass through Plitvice. The lines you might look at are the lines from Split - Varaždin or Split - Zagreb, because they pass through Plitvice.
A good page to get started is the page displaying info for Plitvice bus terminal: http://www.autobusni-kolodvor.com/en/terminal.aspx?k=356&d=191
Click for example on Split - Varaždin and you will see a popup window with the towns the bus passes through.
Hope this helps you plan your trip. almost 10 years ago