pdf ebooks can not be opened/read -- please help

I bought 2 pdf ebooks from amazon in 2005. Back then, reading them with Adobe reader 6 was just fine. I did not touch the two ebooks in 2006.

Now, I find Reader 6, 7, or 8 can not open these two ebooks. I went a lot a activating process which was guided through to Adobe website. Never works.

Would appreciate any advice on how to open/read these 2 ebooks in other way. Thanks in advance.

Mingyou