Those iPads have a ton of apps preinstalled in the stores. If you don't know anything else try the Notes app. Also keep in mind any Apple retail store has 14 days return policy, and you can use the product in that time to see if it's really for you.
Those demo devices are not allowing anyone to install anything on it. But some pre installed apps are more than enough to demonstrate the capability of iPad Pro with pencil and/or keyboard.
Why doesn't Amazon have the iPad Pro 10.5 inch keyboard in stock ? I prefer to buy it from a store with 30 day return policy and not 14 day return policy.
Apple and Amazon are not friends. Amazon usually does not sell current Apple products unless through a third party.
That sucks.