Actually, you can only upgrade Acrobat 11 to Acrobat 2017 (perpetual license). There is no upgrade path for any earlier versions. You must either purchase a subscription or pay the price for a full new copy of Acrobat 2017.
Update - July 2020: Acrobat 2017 is discontinued. Acrobat 2020 replaces Acrobat 2017.
I feel betrayed by Adobe for the end of life of Acrobat 8. I don't have the kind of money that they want for a subscription or outright purchase. They should be ashamed of themselves.
We are sorry you feel so “betrayed” by Adobe.
Acrobat 8 was released in 2006 (14 years ago) and was replaced by Acrobat 9 two years later. Quite a few changes in technology and the operating systems (Windows and MacOS) and application programs (including Microsoft Office) that coordinate with Acrobat have occurred over the years. Quite a few very significant changes were made to Acrobat in the ensuing years to not only provide new features, but to maintain compatibility with other software and to address the constantly changing security issues.
When you license Adobe's or any other software, you typically license it for the software and hardware environments that were current at that particular time. In the case of Acrobat 8, that environment was 32-bit Windows XP, much earlier versions of MacOS (that no longer run on current Macs), and Office 2003. Is that your current enviroment or do you have a newer computer, newer OS, and/or newer application versiosn?
No software or hardware vendor provides for indefinite support including free updates to account for long term changes in the technology landscape. And this is true for other types of products as well. Do you expect a free modification to a 1970's era automobile to allow it to use unleaded gasoline or to meet current air pollution standards and fuel economy standards? I would expect not!
Adobe did much more than just stopping support for Acrobat 8, though. It disabled the activation servers for it and pulled the non-activation installer it once offered. Thus it prevented its customers from using it altogether, regardless of whether they have a supported operating system or not. It simply can't be used any longer, unless it happens to have already been activated. That is unconscionable, and in my opinion should also be illegal.