Adobe Acrobat 8 Professional is a legacy product that has reached its end of life and is no longer supported by Adobe. Even if you possess a legitimate activation key or serial number, the activation servers for this version were retired years ago, making it impossible to activate the software through standard online or phone-based methods. Key Limitations for Acrobat 8
Subscription Model: Current versions are available via a monthly or annual subscription through your Adobe ID account. Activation Key For Adobe Acrobat 8 Professional
If you still have your original purchase information, you may be able to find your records, though they will not bypass the activation requirement: Adobe Acrobat 8 Professional is a legacy product
What is an Activation Key?