FTP Bluetooth and STM32F4
FTP is a network protocol which must be implemented over a TCP/IP network. It is not typically used to transfer files to/from Bluetooth devices.

Transferring files to/from a Bluetooth device is usually accomplished using the Bluetooth OBEX (Object Exchange) protocol.

The Bluetooth HC-06 module only supports serial communications; it does not implement OBEX. Other Bluetooth modules might, though.