A digital planner is a digitised version of a traditional planner in form of a hyperlinked PDF. You need a PDF annotation app like Goodnotes, Notability, or Noteshelf, Xodo. These digital tools can help you keep track of your yearly goals, monthly progress, and daily tasks. You can write, draw, doodle as you would be able to do with your paper planner. You can also erase and fix mistakes easily, which is a huge advantage.