One of the most popular methods of monetising an app is to offer selected content as paid, downloadable In-app Purchases (IAPs).
You can make documents in your app available as IAPs.
To make your document available as an IAP, follow these instructions: How to: Publish or Update a Document.
During this process, select Paid for under the Document Availability heading.
Once you have made your document available as an IAP, you will need to configure your IAP in the relevant platforms' developer portals.
For more information on creating IAP products for iOS and Android, see:
How to: Create Android In-app Purchases