password built in an app for restricted download?
You will have a very hard time getting the app approved is my guess, but you can always try.

It's not clear why you aren't using the newsstand functionality - and that will certainly be on the reviewer's mind when they are deciding if the app store needs another app added to the pile.

Technically, you can offer apps that require payment - see HBO Go, various major league baseball apps, but they all either have a free period to explore the paid content or significant free capabilities to justify being available on the app store.

Unless you can show huge value to some people, you'll be facing a hard sell once it's time to get it past review. If you can, start by submitting a test app to the beta testing review using Test Flight. That will only cost you $100 and the time to develop the initial version of the app.

From there you will have a dialog with the review team to judge if or how they will respond to your specific app.

All the above goes out the window if you are selling the app B2B and your purchasers are only VPP businesses. Then you have a great business model and chance for success selling a custom business app.