Eu não quero machucar o dedo na porta.

In Portuguese, body parts are very often used with the definite article, not a possessive, when the owner is obvious from context.

So machucar o dedo naturally means hurt my finger here, because the subject is eu.

Using meu dedo is possible, but it usually adds emphasis, contrast, or clarity:

• Eu não quero machucar o dedo na porta. = normal, natural
• Eu não quero machucar meu dedo na porta. = more explicit, maybe emphasizing my finger

This is a very common pattern in Portuguese:

• Lavei as mãos. = I washed my hands
• Quebrei o braço. = I broke my arm

Na is the contraction of em + a.

• em = in / on / at
• a = the feminine singular article
• porta is feminine, so:
  • em a porta becomes na porta

This kind of contraction is extremely common:

• no = em + o
• na = em + a
• nos = em + os
• nas = em + as

So na porta literally has the idea of in/on/at the door, depending on context.

Because after querer (to want), Portuguese normally uses another verb in the infinitive.

So:

• quero machucar
• quero comer
• quero sair
• quero dormir

This works much like English want to ..., except Portuguese does not use a separate word like to before the infinitive in this structure.

So:

• Eu quero machucar = I want to hurt
• Eu não quero machucar = I don’t want to hurt

Because the sentence is focusing on the body part as the direct object: o dedo.

So:

• machucar o dedo = hurt the finger / hurt my finger
• me machucar = hurt myself

These are related, but not identical.

Compare:

• Eu não quero me machucar. = I don’t want to hurt myself.
• Eu não quero machucar o dedo na porta. = I don’t want to hurt my finger in/on the door.

In the second sentence, the thing being directly mentioned as injured is the finger, so me is not necessary.

Yes. In Brazilian Portuguese, subject pronouns are often omitted when the meaning is clear.

So this is very natural:

• Não quero machucar o dedo na porta.

Including Eu is also correct, but it can sound slightly more explicit or emphatic:

• Eu não quero machucar o dedo na porta.

You might include eu if you are contrasting yourself with someone else:

• Eu não quero machucar o dedo na porta, mas ele não se importa.

Quero is the first person singular present tense of querer.

So:

• eu quero = I want
• você quer = you want
• ele/ela quer = he/she wants
• nós queremos = we want
• eles/elas querem = they want

With negation:

• eu não quero = I don’t want

So in your sentence, quero matches eu.

Yes, dedo can refer generally to a digit, but in normal usage:

• dedo by itself usually means finger
• dedo do pé specifically means toe
• dedo da mão specifically means finger

In this sentence, because of the context of a door, dedo is naturally understood as finger.

This is one of those places where Portuguese and English do not match word-for-word.

Na porta can cover several ideas depending on context. In this sentence, it means the injury happens involving the door.

Depending on the situation, English might say:

• in the door if the finger gets caught
• on the door or against the door if the finger hits the door

So na porta is broader than one single English preposition here. The exact image comes from context, not just the preposition.

It is grammatical and understandable, yes.

But if you specifically mean get my finger caught in the door, Brazilian Portuguese often uses a more specific verb, such as prender:

• Não quero prender o dedo na porta.

If you mean the door crushes the finger, you might also hear:

• Não quero esmagar o dedo na porta.

Machucar is a more general verb meaning to hurt / injure, so it works well if you just mean causing injury without focusing on exactly how.

In standard Portuguese, não usually goes before the verb it negates.

So:

• quero = I want
• não quero = I do not want / I don’t want

That is why the sentence says:

• Eu não quero...

In spoken Brazilian Portuguese, you may sometimes hear patterns like quero não, but that is more colloquial and carries a different tone or emphasis. For a neutral, standard sentence, não quero is the expected form.

Machucar is a common everyday verb meaning to hurt, to injure, or to bruise, depending on context.

Examples:

• Machuquei o joelho. = I hurt my knee.
• Não machuca! = It doesn’t hurt! / That doesn’t hurt!
• Ele machucou a mão. = He hurt his hand.

It is a very useful, general-purpose verb. It is less formal and more everyday than some alternatives like ferir.