Original may be something like the first instance of an artifact. So an original hand-written letter may be the piece that carries the writer's ink. But, what about a letter written on a computer? Is the original the electron configuration on the hard disk? How can the original be distinguished from a copy, in that case?
You could look at Walter Benjamins essay The Work of art in the age of mechanical reproduction for context.
It's actually an old problem; for example lithography allows for prints, so which of these can one say is the original; are they all originals? Studios get by this problem by having a limited run of prints with each being signed to authenticate it.
In the digital realm this isn't going to work since copying is essential to it; to transfer a digital picture from this computer to that computer means to copy it from this computer to that computer, and then to delete the 'original'.
I can't help but agree with Dan here. This going to entirely depend on your view on the matter and whether it is the atoms or not.
In your given situation though, my personal view is that the original version of the writing on the computer, is the initial thoughts in the writer's mind. Although saying that, you could potentially trace that back further and say that he has only written those things due to personal views and experiences, so are they the original concept for the idea?
As indicated already, I think the true definition of something original is something we hold personal, and will differ from matter to matter.