For hosting common files it's ok. Also it is on Android too do, great to transfer files between your Windows and your phone. But if you want better security you have to subscribe a monthly offer.
Dropbox - Online Sync and File Sharing
Sumatra PDF - Sumatra PDF is a slim PDF/DjVu/EPUB/XPS/CHM/CBR/CBZ/MOBI viewer for Windows.
Google Drive - Access and sync your files anywhere
Haihaisoft PDF Reader - Haihaisoft PDF Reader is the name of a free to use PDF reader and printer that is extremely simple to launch.
Mega - Secure File Storage and collaboration
calibre - Ebook manager, viewer & converter