The flash card feature is great. Improving on that I would suggest questions tab. It is basically a feature linked with Highlighter. When we read a PDF document we mark important lines with the Highlighter. The new feature let's you add a question to the highlited segment and the question is displayed on the side. When revision of the topic is required and flashcard or in this case questions revision tab is activated the highlited portion (I.e. The answer to the question) should be opaque and the reviewer needs to attempt questions like a flash card. Based on his satisfaction of the answer, he should be able to rate each question as easy good Hard like in a flash card