How to transfer file to iphone?

[amitabhbansal]

I have attached a hdd with airport extreme dual band base station router, by filebrowser app i can access the hdd and see the files, but i want to copy from hdd to iphone directly, please tell me which app is best for it
Thanks

 

[maflynn]

I use dropbox

 

[amitabhbansal]

But how to connect the hdd with dropbox?