As far as I've seen/read you can't get full-on permanent burn-in. You can get some mild ghosting that takes 1 to 5 page turns to get rid of if you leave an image on the screen too long, depending on how long you leave it on there, but I haven't seen anything permanent. Like you can see a blank spot that is darker than the area around it and you can tell something was there at some point, but a few page turns/refreshes later it is gone. Really hasn't been a problem for me.
For the HTML files, on my reader I've just been opening up the HTML right in Word, you don't have to copy-paste, then just set the page size in Word and save that file as RTF and it reads fine on my reader.