Strokes often result in difficulties with visual focus and tracking, which would make it difficult to read long documents. Visual therapy is a branch of optometry that seeks to address these types of challenges through what is essentially physical therapy for the eyes.
There is also software that can help with visual tracking when reading, including the tools developed by my startup. [1] We were actually unaware of the benefits our tools would have for stroke survivors until we heard from them.
My friend, the stroke victim, has significant difficulty several months following his stroke; he is improving but progress is glacially slow. He has some control and movement on his left side--for example, he can move his arm. He has no movement (but recently some sensations) on his right side and right arm.
He can speak and converse but he's not as quick as he was before the stroke. He no longer needs to search for his words and he is able to talk about the issues of the day. In the beginning, he struggled to formulate sentences; not so much now. He does speak with a low volume and may slur some words because he still does not have full control of his facial muscles. He has some paralysis in his face (left side).
He has limited head and neck movement. He has control of movement in his lower legs and feet but not his body proper. I do not know the extent of is paralysis but he has no obvious mobility. When seated for a long period of time he complains of pain in his buttocks.
This all is from personal observation; I am not privy to his medical reports.
I have never had a stroke, but I have had a serious heart condition that lead to hospitalization. When I got out of the hospital, I had some issues. Mobility was a huge one - I will never forget the first day of 'rehab' when I decided to walk about two kilometers home from a coffee shop. About halfway, I heard these two older women coming up behind me. One used a walker. I tried my absolute best to keep up with them but I couldn't. They passed me like I was standing still and the effort of trying to beat the woman on a walker was so extreme that I had to sit down. Hell, I almost called my Mom at work to get her to come and drive me the rest of the way home.
There I was. 40 years old. Lying on the fucking grass on the side of the road. Genuinely asking why I had to survive if this is what life was going to be like.
I had to rehab two things. I had to rehab my body, but first I had to rehab my brain. I have never and will never forget the feeling of 'used to' while I was rehabbing my body. I 'used to' be able to run. I 'used to' be able to walk faster than little old ladies on walkers. I 'used to' be able to eat whatever I wanted. I 'used to' be able to mow my fucking lawn. I 'used to' be able to walk up a flight of stairs without taking three breaks on the way. I was paralyzed by 'used to'.
You're his friend so honestly, the best advice I can give you is to encourage the hell out of him. It sounds like he has come a long ways. I have no idea what rehabbing a stroke would be like, but I assume that it's significantly worse than rehabbing a heart. If it is actually worse than rehabbing a stroke, your friend is fucking hardcore. Seriously...this man has come an incredibly long ways and deserves some serious praise.
I'm a sample of one, but that kind of praise really helped me. Every single thing about rehab sucks. Praise makes it suck less.
Edit - I'm much better now. Hell, a few weeks ago, I told my psychiatrist that I was in serious danger of qualifying to run the Boston Marathon by the time I'm 45.
Your friend sounds like a candidate for speech-to-text software. I did work for a woman with MS who was paralyzed from the neck down. She used the Windows 7 accessibility that's built in as her only interface to the computer. Despite her difficulties and advanced age, she was able to make good use of it not just for typing but for overall computer control. I'd hope that the W10 stuff is better yet.
If he has any use of the keyboard, then some hotkeys/macros with AutoHotKey may make his life easier as well. I once used AHK to disable the right mouse button for my grandfather, who before he passed, lost dexterity in his hands and was whole-hand clicking rather than just with his index finger. Disabling the button was easy, and I just re-mapped it to a key he never used (NumPad+).
Most important question: what does your friend want to do that he can't? You're describing his limitations, not his goals. Does he want to read, but not write? A Kindle might be better than an iPad - longer battery life. Does he want to read, but not have to raise his arm to do the page turn? Then back to iPad but using a switch device that can be operated from one finger.
I'm not explaining this well, because I'm a technologist, not a therapist: in the UK the role would be "Occupational Therapist". However, in my experience, they are focused on improvement and the regaining of function: only when this avenue is exhausted will they begin to look at assistive technology. But I am probably being unfair.
Sorry, it's late, and I am a n00b. You wrote email and editing.
Your friend's problems are largely about control and typing. They may be able to use one arm, but it may tire fast. Consider alternative mice, including trackballs. A keyboard if possible, perhaps a tablet with keyguards. If not, some kind of switch control for an onscreen keyboard: it will be slow but maybe more useful. One Switch Mouse, above. Built-in features, like Windows here:
https://support.microsoft.com/en-gb/help/27936/windows-10-ma...
Eyegaze: cameras that track where you are looking. Hard to use, probably not best if your friend can use an arm.
Speech recognition: you really want Dragon Professional on Windows. If you can't get a trial of that, macOS speech recognition. You MUST MUST MUST have a decent mic. Windows 10 machine, try Windows Key + H in an edit box, or this freeware (my employer again):
https://www.clarosoftware.com/login/admin/labs/#clarodrake
Your friend is still regaining function, which changes the dynamic: using the built-in features, maybe with a trackball, might be best until you know where they end up. Again, this is an OT call.
If it's practical, the most helpful thing might be to connect your friend with a good occupational therapist. They have experience and expertise with the sorts of affordances implied by your description. Good luck.
He has several therapists for different problems. Ideally he would be in therapy all the time, but the economics are impossible. As it stands now, he gets therapy several times a week. Clinical studies seem to indicate that is too little for rapid progress.
I'm working on a Chrome Extension that lets you open tabs, navigate pages, click links, dictate emails etc. on the web using voice-control: https://www.lipsurf.com
Many of my users have motor control issues. Depending on the manner of the difficulty, I think this will be useful to you.
There is also software that can help with visual tracking when reading, including the tools developed by my startup. [1] We were actually unaware of the benefits our tools would have for stroke survivors until we heard from them.
1: http://www.beelinereader.com