Develop a secure online system for storing, retrieving, generating and marking up documents (mainly PDFs). Development of dedicated mobile app.

I need someone to develop some software for my business. I am looking to develop a secure system which multiple users can use to store and download/view documents in an organised way (mainly PDF but other documents too). The system should be developed to be accessible on both computer desktops but also mobile platforms (iOS preferably or android) through a dedicated app for the system. The system should be also be able to provide basic annotations to pdf documents(all internally). The system would require multiple users to be able to login securely to the system with their own dedicated accounts. Users should be able to communicate with each other through the system (not live) but through messages/attachments and e-mail notifications should be sent to users emails when messages are sent/received. Users then log on to view responses. The program must also be allow users to create custom question forms (to be answered with yes/no/comments/pictures answers) that when completed by users will output a PDF file showing everything which can then be stored securely in dedicated areas on the system or automatically e-mailed to certain users. These forms should be able to be generated on the desktop system but only need to be answered on the mobile system. The software must be modern with a lot of further capability for expansion and extra functionality. The data stored on the system must be extremely secure.