sending files from android to arduino

right now i'm working on an arduino project in which i have to create an android app that must send files to arduino sd card using bluetooth

the app can easily connect to arduino using hc06 and i can send data to it

for example i can send '1' and '0' to toggle led,'3' for temperature and humidity (DHT11) and '4' for heartbeat (KY039)

but when it comes to a file i'm really confused because i don't know how i can send a file from my phone and put it in arduino sd card