Using a simple URL scheme you can link to a particular edition within an app and even a particular page. The URL scheme is apparent during the building of the App and can be provided by your App Technician.
Link to the latest edition
So, to link to the latest edition within the app from outside the app, you would use:
with URLscheme being replaced with your own App URL scheme.
Link to specific page
To link to a specific page within an app, you must know the Node ID (see 'What is a node id and why is it important?') and the page that you wish to link to, then it is a case of using the following link:
When clicking the link from another app, if the App is already installed, it is launched, and a) if the edition is downloaded, then it is opened or b) if not downloaded, the download/purchase edition page is shown.