How does file transfer work?
With the file transfer system is it obfuscated who the sender and receiver is, mixing like the coins?
Is file permanently or temporarily stored on blockchain?
As far as I understood they use InterPlanetary File System (IPFS) for the encrypted file to store and only send a hash of it in the bc.
So it is totaly anonymous
Detailed Infos should be in the blog post:
https://blog.ultranote.org/attachment-feature-added-to-gui-wallet/