You don't need to do anything to use the DR1000, it works in any country. You can register on the irex website, but quite frankly I don't know why you need to. In theory it just allows irex to advise you of updates.
pdf support is excellent, or better than others I have tried largely due to the size of the display and you can write all over them
It doesn't support chm natively. I don't know if fbreader does, but if it does, fbreader has been ported to the DR1000 and so it would be able to read them.