Can I attach files to a secret note?

Yes. Attach files when creating a note and each one is encrypted in your browser before it uploads — the file contents and even the filename reach our servers only as scrambled ciphertext. The recipient's browser downloads and decrypts them with the key from your link, which we never see. Files follow the note's fate: when the note burns or expires, its files are destroyed too (after a burn, the reader gets a short window to save them).