It could have been use full if you have mentioned the whole problem you have. I will try to answer the best I can:
Solution One: You can maintain a shared memory for the Raspberry pi and Arduino board. (It can be some external SD card). Get the code from the cloud using Raspberry pi and write this using file streams into the shared memory. Then read this file from the same shared memory using Arduino.
Solution Two: If you are not worried about the exact file and your only concern in the logic, interface the Arduino to Raspberry pi as a slave device. Use the Arduino I/O ports to read the digital signals or values from raspberry pi which are generated according to the code you got from cloud using windows10 IOT platform.
I hope this could help you to some extent.