in iOS devices, the Mail app offers "Open In..." option for attachments. The apps listed have registered their CFBundleDocumentTypes with the OS. What I am wondering is how my app might know, for a given file type, which other app could open it ?
There is no public API for this, however, you can open the sheet that Mail.app shows using the UIDocumentInteractionController class. It doesn't give you access to the names of the Apps that can handle the document, but its probably better than nothing.