Flash built app with in-app purchases using Adobe AIR

I am working on building an app using flash which will run on desktop/ios/android, using adobe air to publish the final content. I am pretty proficient using flash, but not so much in actionscript.

The idea for the app is one of a library where a user can read a free book (short story really) and then have the option to purchase other stories via in-app purchases.

Does anyone know how this would work best? Should those short stories be located in separate movie clips within the app and are just locked and invisible until the user makes payment? Then when paid they are made visible for the user to read? Or should be be held somewhere externally? Maybe in PDF form, so when the user purchases then they can view the pdf within the app?

Or what would people recommend?

Thank you in advance for any help/advice!