How to draw on a PDF file
Buy a drawing tablet (although you may be able to find used ones) and download an illustration app. Purchase or make templates of shapes you want to draw that are the same size as the drawing area. Set your main aim or target in mind, such as a house, car, bus for kids learning to read and write letters, etc. Find different photos/shapes from Google images (or use words). Bring them into your preferred drawing app and place them over on a blank canvas with guides where it needs to go within the shape template. Go trough each line with your finger on the tablet – your physical movement will move the digital pen on screen which does not require any physical movements of its own apart from being plugged in and switched on. Start with one line and then move on to the next, until you become more confident with your illustration skills. Draw in a digital notepad (you can create one for free) similar to how we do it when writing an email or letter and this is the simplest way of drawing.