Files/Attachments can be added to Notes in Akita.

Navigate to the relevant Account Record and then to the Activities tab.

Either create a new Note and the click into it OR click into an existing Note. The Note record will appear on the right-hand-side of your screen.

To add a file, either drag-and-drop it into the Attachments section or click on the Attachments section, search for your file and add it [as per gif below].