Can we imagine life without Adobe Reader? Certainly I can not.
You require this application for books, bills, notification and what not. This is quite portable and can easily convertible to ms word and ms word can easily convertible to adobe reader too.
Files take less space and most importantly is free. It saves a lot of papers cause now everyone have it everyone cant transfer adobe files over the internet.
Now they have come with many new feature like. one can export pdf to cloud storage. one can edit the file and create it too.
You have to create an account for many others tools like. send for signature and other editing options.