I have been using Notebooks for several years now and I have found it very useful so manage numerous files of all types: store them, tag them, retrieve them, annotate them (especially pdf). The app has helped me prepare articles, presentations, and even a couple books. It has improved regularly over the years and works smoothly with dropbox. Nothing more to say than it is a great app to work with documents. It has never failed me. Wrote this a year ago; have not changed my mind, still the best