Store any kind of sensitive text in an encrypted database ,
the encryption key alow you to decrypt and view the stored text only inside the app,
so no one can view or read the contenet inside the app without this key.
you can also save the databas as a secure file in a folder on your phone ,
also you can share it with others via bleutouth,mail…
in this cas the encryption key should shared with them too to accesse the contnent of file.