Eu preciso renovar um documento este mês.

Yes. In Brazilian Portuguese, you can often omit the subject pronoun because the verb form already shows who the subject is.

• Eu preciso renovar um documento este mês.
• Preciso renovar um documento este mês.

Both mean the same thing: I need to renew a document this month.

Including eu can add:

• emphasis: I need to renew it
• clarity, especially in conversation
• a slightly more explicit style

So eu is correct, but not always necessary.

Because preciso is the conjugated form of the verb precisar for eu in the present tense.

The verb is:

• precisar = to need

Present tense:

• eu preciso = I need
• você precisa = you need
• ele/ela precisa = he/she needs
• nós precisamos = we need
• eles/elas precisam = they need

So in this sentence:

• Eu preciso = I need

Because after preciso, the next verb stays in the infinitive.

This is similar to English:

• I need to renew
• Eu preciso renovar

In Portuguese, you do not add a separate word exactly like to before the second verb here. The structure is simply:

• precisar + infinitive

Examples:

• Preciso estudar. = I need to study.
• Preciso trabalhar amanhã. = I need to work tomorrow.
• Preciso renovar um documento. = I need to renew a document.

This is a very common question, because precisar can appear in two patterns:

1. precisar de + noun

   • Preciso de ajuda. = I need help.
   • Preciso de dinheiro. = I need money.

2. precisar + infinitive

   • Preciso renovar um documento. = I need to renew a document.
   • Preciso estudar. = I need to study.

So:

• with a noun, you often use de
• with a verb, you normally do not use de

That is why the sentence is:

• Eu preciso renovar... not
• Eu preciso de renovar... in standard Brazilian Portuguese

Because um means a/an, while o means the.

• um documento = a document
• o documento = the document

So um documento is used when the document is not being identified as a specific one already known in the conversation.

Compare:

• Preciso renovar um documento. = I need to renew a document.
• Preciso renovar o documento. = I need to renew the document.

If the listener already knows which document you mean, o documento would make more sense.

Yes, you could also hear esse mês in Brazilian Portuguese.

Traditional grammar often teaches:

• este = this, near the speaker
• esse = that, near the listener
• aquele = that over there

But in everyday Brazilian Portuguese, the distinction between este and esse is often less strict, and esse is very common where English would say this.

So these are both possible in Brazil:

• este mês = this month
• esse mês = this month

A useful learner takeaway:

• este mês sounds correct and a bit more formal or careful
• esse mês is very common in everyday speech

Because documento and mês are masculine nouns, and demonstratives/articles must agree in gender and number with the noun they describe.

Here:

• mês is masculine singular
• so you use este

Agreement pattern:

• este = masculine singular
• esta = feminine singular
• estes = masculine plural
• estas = feminine plural

Examples:

• este mês = this month
• esta semana = this week

So it is este mês because mês is masculine.

Yes. Portuguese word order is flexible, especially with time expressions like este mês.

All of these are natural:

• Eu preciso renovar um documento este mês.
• Este mês, eu preciso renovar um documento.
• Preciso renovar um documento este mês.

The meaning stays basically the same, but the focus can shift a little:

• Este mês, eu preciso... puts more emphasis on this month
• Eu preciso renovar... starts with the subject
• Preciso renovar... sounds very natural and concise

Renovar means to renew.

It is often used for things like:

• passaporte = passport
• visto = visa
• carteira de motorista = driver’s license
• documento = document
• assinatura = subscription

Examples:

• Preciso renovar meu passaporte.
• Ela renovou a carteira de motorista.

So in this sentence, renovar um documento means renewing some official paper or ID.

Yes. That is a very common alternative.

• Eu preciso renovar um documento este mês.
• Eu tenho que renovar um documento este mês.

Both can mean I need to renew a document this month.

Very roughly:

• preciso can sound a bit more neutral or direct
• tenho que is extremely common in speech and can feel like have to

In many everyday situations, they are interchangeable.

Este mês is a time expression. It tells you when the action needs to happen.

Sentence structure:

• Eu = subject
• preciso = main conjugated verb
• renovar = infinitive verb
• um documento = object
• este mês = time expression

So este mês works like this month in English.

The accent in mês shows the stressed vowel and is part of the correct spelling.

• mês = month
• plural: meses = months

The accent mark helps indicate pronunciation and stress. Portuguese spelling uses accents much more systematically than English, so they are important and should not be ignored in writing.

A very natural spoken version would often be:

• Preciso renovar um documento esse mês.

Why?

• dropping eu is common
• using esse mês is very common in Brazil

But the original sentence:

• Eu preciso renovar um documento este mês.

is still completely correct and natural, especially in careful speech or writing.