Learn Portuguese (Portugal): De acordo com o médico, estou bem.

Yes, absolutely! Segundo and de acordo com are interchangeable when they mean "according to". Segundo is just a single word and can sound slightly more formal, but both are completely natural in everyday Portuguese.

Could de acordo com also mean "in agreement with"?

Yes, it can. In this sentence, because it's at the start and followed by a comma, it clearly means "according to the doctor". However, if you changed the sentence slightly to estou de acordo com o médico, it would mean "I agree with the doctor".

Why do we use estou instead of sou for "I am" here?

We use a form of estar because health and how you feel are treated as temporary states or conditions. You use estou to say how you are doing right now. If you used sou (from the verb ser, used for permanent traits), it wouldn't make sense for describing your current health.

I often want to translate "I am good" as estou bom. Why is estou bem used here instead?

In Portuguese, to express that you are doing well or feeling fine, you must use the adverb bem (well). If you say estou bom, it usually implies you are specifically cured of an illness, or in certain slang contexts, that you are physically attractive. Estou bem is the standard, natural way to say "I'm fine".