Develope an Online Based Template Software

I want to create a online based software. Clients login, and enter the program. They are asked a series of questions. Their answers are then placed in a particular spot in a final PDF document that is all based on their choices and entries. They will have some questions that are basic enter text, some that are drop down boxes that based on their select causes particular tests to be in the final document and there will be numbers questions that based on what they enter formulas similar to that of excel will be run to create charts and tables. This will also require a web based management to it. Thus a client login where they can access the program, save there progress, and view their completed works. They also should be able to contact us via message in it. There would also need to be an admin side where we can add and remove clients, view their messages, and there documents they create. This will be all behind a front end squeeze page like [login to view URL] that is integrated with paypal so they can select and purchase right there.