Is it possible to send files(.mp4 .mp3 pdf etc) between my arduino and my android phone through bluetooth, and store them in an SD card?
Sure. Will be slow. A song for example is 5 to 8 Megabytes. Arduino running at blazing speed (SPI at 8 MHz clock and doing nothing else) can do almost 1 byte/microsecond (17 clocks, vs 16 clocks/uS), so taking into account it getting the info from another sources, sending it to Bluetooth, and then Bluetooth sending it out, you ending up handling the info 3-4 times before the android gets it. So maybe 4 uS for each byte effective. With good coding, someone ljke fat16lib writing it. So 1/16000000 * 17 * 4 * 8000000 = 34 seconds or more as an estimate. Compare to USB2 where it takes about a second/song to transfer a file from a PC to a portable hard drive.
Please can someone help me with some source code that will enable me to send files to my arduino via bluetooth and store the files on an SD card, or sites where I can get one .. Cos for some months now I've being trying on this, a little sample will do.. Thanks..
For Bluetooth, I found http://tronixlabs.com.au/news/tutorial-using-hc06-bluetooth-to-serial-wireless-uart-adaptors-with-arduino/ very easy to understand.
Similarly, https://www.arduino.cc/en/Tutorial/ReadWrite for SD card writes.
You will need to post your code for people to help you.
No one here is going to hand you ready-made code.