Looking for a reader for multiple PDF files at once

Question

To use in private flight training domain, highly demanding on documentation, I am looking for a PDF reader on Android tablet (vertical portrait mode) which is able to manage several open files at the same time. Navigation between the documents should be done by sliding your finger across the screen, which provides fast access to information:

1. The vertical navigation displays successive pages of the visible document
2. The horizontal navigation displays successive documents

I tested a few PDF readers, but did not find one which could open several files at once.

Do you have any suggestion ?

Thanks for your help !