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
FoxyUtils Online PDF Tools - All the PDF tools you need! Save time with our easy to use online tools to merge, split, convert, and edit PDF files.
Google Drive - Access and sync your files anywhere
PDF Reader Pro - PDF Reader Pro is an all-in-one PDF office supporting to Read, Annotate, Edit, OCR, Convert, Create & Fill Form, Sign PDFs, TTS on Mac, iOS, Android, and Windows.
Mega - Secure File Storage and collaboration
Easy PDF - EasyPDF is a free online PDF conversion suite that can help you convert & create PDFs. Securely, anonymously and without any limitations.