Can I securely share files in the tool?

At this stage, no. The current version is in beta and among other things, it lacks the multi-user support which would enable the secure file sharing. 

We are working hard on the release of the public version though, and this one will allow you to invite others to a specific Bernstein project, where they will be able to access to the files only with your specific approval (granted through your encryption key) and the input of their own, linking them to the knowledge of the files in an indisputable way.  

However, you can use blockchain certificates to enhance NDAs, improving the way you share data with other parties.