Eventually will I have to pay for using any of this

Hello Christy, 

I hope you are doing well. As per the above description, I understand that you want to use the Acrobat Reader Mobile Application.

The application is free to use; however, certain features need you to be subscribed to a plan so you can use them. It depends upon your usage of the application and whether you need to pay or not.

You may check the link to learn more about the subscription feature:Manage subscriptions — Acrobat for iOS Help (adobe.com)

Let me know if this helps.

Thanks,

Souvik.