When I hit Activate it says: "Activation was unsuccessful because the activation server is not available at this time. Please do one of the following.."
In the past when I had a similar problem I called Adobe support and they were able to fix the issue. I haven't read the link the other poster provided, so that may be more current information.
Read the thread https://community.adobe.com/t5/acrobat/adobe-acrobat-7-0-standard-activation-locked-dead-program/td-... that @JR Boulay has pointed you to. Simply stated, you can no longer activate Acrobat 7. The activation servers were decommissioned a number of years ago and that version of Acrobat only fully and properly installed and ran on Windows XP, a version of Windows that hasn't been supported by Microsoft for a number of years now.