Arial is a bizarre case: it's actually Monotype Grotesque stretched and pinched to match the proportions of Helvetica. So you can replace Helvetica with Arial

Arial is a bizarre case: it's actually Monotype Grotesque stretched and pinched to match the proportions of Helvetica. So you can replace Helvetica with Arial in any document and it'll still print right, but at its core the letterforms are just distorted Grotesque MT. And it's not the only font Microsoft and Monotype collaborated on like this. For example, Century Gothic is Monotype's Twentieth Century distorted to match ITC Avant Garde's metrics.