Android App Two Page Activity with admob

In our old app we are update, Two Page activity, Book app, One activity is first menu page, when i start a app app connect with firebase and download firebase database to local database, second when i click on menu, open pdf file, that pdf files download in mobile cache. one time download.
in menu page native ads show. and pdf actitivty banner ads show in bottom. when i click X button all ads are hide. Rewars ads show and hide all ads for two hours.
Ads code are already we have. menu and content are there but in this time hard coded in so we want to go our app size reduce. and use firebase for database and pdf or external pdf we used.