Application for manage and sync PDF collection

Unfortunately is not possible synch the PDFs files using iBook, so i'm looking for an alternative. I have a huge collection of PDF file and i work with different computers.

I'm looking for an application that can takes care of all my PDFs and generate an archive that can be put on Dropbox / iCloud Drive.

Sometink like Calibre but possibly with a better UX. It shouldn't be necessarely free.

Thanks.