Yes, A user can add file attachments in the chatbot both when they are in a case context and when they are outside of a case context. When a user is in a case context, file attachments are part of the processed business case. The file attachments are automatically assigned to an interaction case when a user is outside of a case context.
I believe the question was whether the chatbot can send an attachment to the user, not the other way around. The answer to that is that this can't be done directly from the bot to the user's desktop. One good option would be to update the case flow to send the attachment via an email with an automation.