@xundercover9789, the web version of the book requires an internet connection and you have to be logged into hooktheory.com to read it. There is no PDF version of the book. Purchasing web access to the book does not give you any other features other than web access.
The Hooktheory I app for Android/iOS is our book, packaged for consumption on phones/tablets. The look/feel and content between the native apps and the web app are identical. The main difference is that the web app requires an internet connection; native apps download all material with the initial app purchase.
Hookpad, our songwriting software, is not available on iOS/Android right now; just the web app on hooktheory.com.
If that doesn’t answer all of your questions, let us know.