By secure the data do you mean make sure that nobody can see it or is it to ensure that if they need to rebuild/reload the computer that you won't lose the data?

The latter is easy. You can back it up with either a cloud tool (acronis, backblaze, carbonite) or to a service like dropbox, google drive.
The former becomes harder. if you have everything already in the documents library/folder you could encrypt that folder or copy the data of to a drive/service and remove it.