A free app for Android, by U-Shipps.
If you're looking for an easy way to create a workbook for yourself, there's no better app than "Workbook Maker". This application is designed for creating your own workbook. You can create it from various sources such as notes, books, PDFs, and more.
The application allows you to import documents with a camera, scanner, or other methods. Once you import the document, you can hide the place you want to remember with a check pen. To memorize the answers, you have to tap on the hidden place.
If you have a workbook that you need to study, this app will help you do that.