(1) Delete multiple PDFs on Android Tablet -- (2) Which Reader for This Device?

I found an "ALL" icon yesterday, but today it has disappeared.  I downloaded a different Reader, but no luck.  Which brings me to my TWO questions:

(1) Which PDF Reader is best for my Samsung Android Tablet?  - and -

(2)  How do I delete multiple PDFs at one time on this device (Android Tablet)?