Is it necessarily better to read something online as opposed to a regular book? Either way, you are reading which is good but wouldn't reading online have the same effect on you as watching tv all day. the way your eyes get sensitive and everything.
Reading online has its benefits, as revealed in the article that we tend to get through pieces faster when we are viewing them online, however there are a few drawbacks, as pointed out. We grow tired faster from reading online because staring at screens for too long makes your eyes grow fatigued.
For my annotations, I used adobe which worked out fine. I tried downloading some pdf annotator but those have trial fees so stay away from them. Adobe allows you to highlight anything you want and create side bubbles for commentary. the only downside to Adobe is the glitches which will give you trouble if you try to attach files or pictures, or in this case, it doubles them, sorry about that :)