I need answer to some questions that are not clear from your post.
Are you an existing customer?
Which version of Forms you are trying to evaluate?
AEM Forms is available in two technology stacks, AEM Forms OSGI and AEM Forms JEE (formerly LiveCycle). It would depend on your use case which stack you should choose but I would suggest using AEM Forms on OSGI stack if you are not an existing customer of Livecycle as new features are being added to OSGI stack with every release.
Instructions to download and install AEM Forms on OSGI stack can be found here.
Instructions to download and install AEM Forms on JEE can be found here.
Differences between the two offering can be found here.
Now, coming to your question of how to install Reader Extensions, when you install AEM Forms on OSGI stack, Reader Extensions module is by default included in it. You need to follow this article to configure your Reader Extensions service.
When you install AEM Forms on JEE and follow the mentioned article, you have the option of choosing which components to install and Reader Extensions is one of them.
I hope it clarified your doubt. If you have any more questions, please post them here, Adobe will be happy to help you.