If it was normal matter you'd be able to see or detect it, like all the other matter we can see and detect, dark matter is something predicted to be there because something currently undetectable is affecting the matter we can see and detect.
so as and when we find the dark matter it wont turn out to be normal matter (protons, neutrons, electrons, photons) but something else cool like a whole load of new particles, because we have already detected/accounted for all of the normal matter in the entire universe?
If it was normal matter you'd be able to see or detect it, like all the other matter we can see and detect, dark matter is something predicted to be there because something currently undetectable is affecting the matter we can see and detect.