A contraction of ditto, which is the Italian détto (said), Latindictus.
How do you do? i.e. How do you fare? It should be, How do you du! (Anglo-Saxon, dug-an = valēre); in Latin, Quomodo vales.
Well to do. This, again, is not the transitive verb (facĕre) but the intransitive verb (valēre), and means “well to fare.” (Anglo-Saxon, dug-an = valēre.)