As far as I know, in Mendix 7, files are synced and downloaded according to your permissions. If you wish to open these files in an external app, you will need to build your own widget for it. Make sure to store the correct mime type, as Android and iOS will need these to open the file with the correct app (PDF → PDF Viewer, DOC → MS Word or Google Docs, etc.). Once the files are open in an external app, you can use that app’s built-in share functionality. For example, if a PDF is open in the Google Driver PDF viewer, it is easy to store in on your Google Drive, or share it via Email.