Your app is a consumer (you said you are importing.) Apple's Gallery app is also a consumer AND a producer. As a producer, Gallery could share with your app as a consumer.
On the desktop (OSX) declaring the UTI's that your app supports (produces or consumes) in your app bundle is the first step. Then in what is similar to 'sharing', the Finder lets you double click a file (document) to open it with the default app (or other app) that supports the UTI. Finder is part of security (sandboxing): the user is in charge when using the Finder and the OS assumes the user understands the security implications of sharing content between apps, but the Finder may still give warnings about security.
On iOS, I suppose you are asking whether declaring UTI's in your app bundle is sufficient for the Share button? I don't know. In iOS8 apparently you need an App Extension.