CS3, Acrobat Pro 8 update unavailable?

I can only find old and out of date posts relating to this problem.

I am using (at work, no choice in the matter) a late 2006 iMac with legitimate version of CS3, inc Acrobat Pro 8.0.0.

The original licence does not work, so I was forced to download a version of CS3 from Adobe with a new serial key that Adobe supplied.

I cannot update Acrobat Pro from 8.0.0 to anything else. There is no "update" option in the menu bar at all.

Is there ANY WAY that the software might be updated? I am experiencing problems in proofing PDFs, which is what I need to do. On a similar machine with the same software but 8.3.1, I am able to proof without issue. The actual problem is when I highlight text to comment and markup, it highlights in a MASSIVE way, i.e. like 50pt highlight on 9pt text.

Any help or guidance would be very much appreicated.

The Adobe update website does not appear to go back further than Acrobat Pro 10.