The e-ink technology is like dynamically printing a page every time you 'click'. As you go page by page, the screen is erased and then the next page is "printed". The system uses tiny particles suspended in a liquid, so it is very much like actual ink.
There is NO backlit display, as none is needed. You can read for hours without any eye fatigue. Think of it as the ability to buy an electronic paperback, and then being able to print each page on demand, using the same space.
Like a paperback, you can definitely read in bright sunlight; the only thing you would want to avoid is a position where the e-reader is reflecting the sun directly back into your eyes. Like a paperback, you would need some other light source if you are reading in a dimly lit room.
The Kindle is known for holding battery power a long time, and is better than the Nook at that. The more reading you do, though, the quicker the battery will wear down, but each charge is good for many, many hours of reading. Since the power consumption is very low, I have never noticed any heat issues.
PDF files can be read, although they are not always ideal as they sometimes don't get the paragraph breaks right, and resizing of fonts doesn't always work well. I have converted them to other formats for better results. For example, "Midnight Sun", a protected PDF file, was a pain to pull out into Word, but I was eventually successful and inserted a Table of Contents, and then converted to epub for my own use and convenience. I believe you can also convert LIT files, but any time there are Digital Rights Management involved, you may have issues.
I have an example for what you can and cannot do with an e-reader, and the differences in viewing them versus something with a backlit display, . I downloaded the fanfic "Wide Awake" that the author generously provided in the Word format. I saved as an unfiltered web page, and then converted to the epub format through the freeware program Calibre. The whole process took only a few minutes, and I now have that story on my Nook and was able to read for hours at a time without any eye fatigue, and I can jump from chapter to chapter and resize fonts without any problem. Another fanfic "Emancipation Procalamation", is only available online through Google docs, and it is protected. I can read it on my Ipod, but the backlit display will fatigue my eyes after an hour or so. I have to turn my reading light on for the Nook, but I don't have to for my Ipod, but the reading experience is much better on the Nook.
"It will take an amazing amount of control,” she mused. “More even than Carlisle has. He may be just strong enough…the only thing he’s not strong enough to do is stay away from her. That’s a lost cause.”