I think the main idea of the text is to say the notary is validating the document despite its lacking the indicia of authenticity that one could infer from the use of handwriting. In other words, the notary is saying one needn't be troubled by the non-holographic format. "By mechanical means" drives home that point better than "typed" or "printed," which would be obvious without the need for any special mention by the notary.

The "mechanical means" point would especially require emphasis if it's a type of document for which the default requirement is handwriting, such as an unwitnessed last will.

La norma contenuta nell'art.51 n.8, secondo inciso, L.Not. ("Il notaro non potrà commettere ad altri la lettura dell'atto che non sia stato scritto da lui, salvo ciò che dispone il codice civile in ordine ai testamenti") viene solitamente intesa in senso restrittivo, richiedendosi, per la sua applicabilità, che l'atto sia stato scritto interamente dal notaio a mano. A mio modo di vedere, però, la lettera della norma è compatibile anche con la scrittura da parte del notaio con mezzo meccanico. http://foro.romoloromani.it/topic/15866-atto-scritto-dal-not...



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Note added at 2 hrs (2017-06-30 19:53:10 GMT)
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It also makes me nervous to discard a common legal phrase merely because it's klutzy, without knowing what traditions or principles historically are associated with it. This is why so much legalese endures despite being awkward. The idea is to signal a judge that "yes, this is the same phrase you've seen elsewhere," should it come to that.

Its a plural sentence in Italian, Mezzo=Mezzi Meccanici=Meccanico