If I use InDesign to create an app, can I create one document for different devices
(eg. smartphone & tablet devices)?
I know I still need to create another version for vertical or landscape orientation.
For different platform, not sure if one file will do this all.
Do you kow?
Ideally you should design separately for different devices. For example if you intend to publish content on iPad 1/2 (Res 1024*768) and Samsung galaxy Tab Res (1232*752), you would need to have files with different dimensions. If you use a single file for example 1024*768, it would appear in Samsung Galaxy Tab, however would not fit the screen as intended and would result in a poor user experience.
You may use alternate layout feature in Indesign CS6 to design quickly for different devices and then use renditions to publish your content for diferrent devices.