CDs and DVDs are not a good method of backing up data, they suffer from what some people refer to as "Disc Rot", where the media will start to get holes in the protective layer. If you have any really old music CDs, you may have noticed it, hold them up to the light you may see some holes forming. I had 20-30 CDs containing old back-ups from around 2000, about 50% of them had signs of CD rot.
Here's an article on it: USATODAY.com - CDs and DVDs not so immortal after all
The best storage medium for important documents is hard copy or non-volatile memory, like flash drives.