The iPad app supports inter-app communication using URLs. At the moment only the command to open a specified project is included.
roomarranger://project/some_file_name.rap- this will open the project already present inside the app (an item in the list under New/Open button - iPad)
To send a new project file into Room Arranger app, you can just open it, and iPad will let the user select Room Arranger as the application to open it with. The project will be copied into the app