Body
One thing that seems to help with screen fatigue, as well as just being a good thing to do anyway for accessibility purposes, is to make sure that your PDF readings are document reader compatible.
A document reader takes text from an electronic document, website, etc. and reads it verbally. This is great for blind people as well as people with low vision, and dyslexia. This can also work for people who process spoken information better than written information. As we all suffer from different levels of screen fatigue, this is also becoming an increasingly utilized assistive technology.