Hi, @PauloVBettio! And welcome to Heroic Labs forum!
Hope you become one of the many frequent contributors we have here. And, please, make sure to read our guideline 
Regarding Nakama’s storage features, the short answer is that it is not meant to store and manage binary files. It could be done through some type of serialization (e.g., base64) but this is NOT recommended.
Also note that using Nakama does not exclude using other APIs along side. Server to server communication could be an option for you.
Hope this helps.
Cheers,
Caetano