I have a 200 page manuscript which I need to translate from English to Portuguese. I am looking for the best software application authors use for this purpose.
Translation is best done by humans. There is no software available to push a button and Make This Portuguese, and even if there is, word-for-word translation simply can't capture the nuance and meaning of idioms and language-specific phrasing. Saying someone "has horns" in European countries means something very specific which doesn't exist in English, for example.
Translation services are a big deal. There are entire companies which do just this, and you should vet and review even their work and not assume it's right.