I have had to re-input Adobe Acrobat on my computer, the product was 8.1 and I am quite happy with this version. However, my license key is showing that it relates to version 8. It will not allow me to download v8, just 8.1. How do I get around this please?
A valid serial number for version 8 should also work for version 8.1 - it's the same major release. Did you happen to change your system recently - perhaps a major hardware or software upgrade? If so, that might nix your license activation.
In any case, something may have gone awry with your licensing. As this is a user-to-user forum, you may not be able to find anyone here with the power to fix licensing issues. Typically you'd have to contact Adobe directly about that:
BTW, note that Acrobat 8 is from 2006 and hasn't received a security update in many years.