You know that saying that if it sounds to good to be true...?
These guys are selling pirated or cracked software, so let your conscious be your guide.
Any particular reason you have to have Acrobat 7? Just curious. I use version 5 at home, and version 6 at work. Some of the faculty at the college I work at have version 7, so I've seen it. To me it's kind of like the different versions of Microsoft Office, more bells and whistles with newer versions, but underneath they all perform the same function.
BTW, Adobe has a download to upgrade to version 8 for $159, almost $300 off of the full price.