Q: When searching text in the PDF document and the input keyboard is open on the screen, it is no longer possible to scroll all the way up to the beginning of the PDF document.

A: This is actually an Android setting. When the keyboard is showing on the screen, Android will adjust the visible portion of the UI, making some content no longer visible.

In order to resize the layout to the available space, you will need to add this option in your manifest’s activity element.

         android:windowSoftInputMode="adjustResize" ... >

Read more https://developer.android.com/training/keyboard-input/visibility.html#Respond