Not sure how it gets such good ratings
Constantly loses connection to Dropbox and won’t keep a PDF file accessible even when offline. Takes forever to load many PDFs that should be locally cached and doesn’t always resume on page I left off on. Maybe it’s good for editing PDFs but not for reading books.
File storage is unfortunately outside our reach. This is handled by the system file picker interface with plugins developed directly by various cloud storage providers. In this particular case, file download and offline caching is provided by the Dropbox application. One way to ensure the files are always available when viewing offline would be to copy the file from Dropbox to local device storage.