There used to be an official Linux version of Acrobat Reader, but it was discontinued a few years ago. In fact, this is quite clearly stated on the very page you linked to:
So, the page you mention simply points you to this very old version that might still be installable. The reason it isn't listed on Adobe's page is that it has been discontinued since 2013, almost 2010 years ago.
As for flash, that is also mostly deprecated, and will be discontinued this year for all operating systems.
