O Pedro diz que o pacote do atum ficou aberto, mas o das uvas ainda está fechado.

In European Portuguese, it is very common to use the definite article before a person's name in everyday speech: o Pedro, a Maria, o João.

So O Pedro diz... is a very natural way to say Pedro says...

This does not make it mean the Pedro in normal English. It is just a standard Portuguese feature.

Que introduces the clause that follows diz:

• O Pedro diz que... = Pedro says that...

In English, that is often omitted:

• Pedro says the package...

In Portuguese, que is normally kept, especially in standard, natural speech.

They are contractions of de + article:

• do = de + o
• das = de + as

So:

• do atum = of the tuna
• das uvas = of the grapes

In this sentence, they help identify which package is being talked about:

• o pacote do atum = the tuna package / the package of tuna
• o das uvas = the grape one / the package of grapes

Portuguese often avoids repeating a noun when it is already clear from context.

So:

• o pacote do atum ... mas o das uvas...

means:

• the tuna package ... but the grape one...

Here, o stands for the omitted noun pacote.

A fuller version would be:

• ...mas o pacote das uvas ainda está fechado.

Both are correct, but the shorter version is more natural because pacote has already been mentioned.

Because o refers to the omitted noun pacote, not to uvas.

• pacote is masculine singular
• therefore the article replacing it is o

So:

• o das uvas = the one of the grapes, where one = package

Even though uvas is feminine plural, the hidden noun is still pacote.

They describe the situation in different ways:

• ficou aberto = ended up open / was left open / became open
• está fechado = is closed

So ficou focuses on a resulting change or outcome, while está describes the current state.

In this sentence:

• o pacote do atum ficou aberto suggests that at some point it ended up open
• o das uvas ainda está fechado says that the grape package is still in the state of being closed

Not exactly.

• ficou aberto means ended up open, was left open, or became open
• foi aberto would be closer to was opened

So ficou aberto focuses on the final state, not directly on the action of opening it.

For example:

• O pacote ficou aberto. = The package ended up open.
• O pacote foi aberto. = The package was opened.

Because they agree with pacote, which is masculine singular.

• o pacote → masculine singular
• therefore aberto and fechado are also masculine singular

If the noun were feminine, the adjective would change:

• a caixa ficou aberta
• a embalagem está fechada

Agreement is very important in Portuguese.

Here, ainda means still.

• ainda está fechado = is still closed

It shows that the situation continues up to now.

So the contrast is:

• the tuna package ended up open
• but the grape package still remains closed

Yes, you might hear pacote de atum, but it is not exactly the same in nuance.

• pacote de atum = a packet/package of tuna in a more general descriptive sense
• o pacote do atum = the specific tuna package already known in the situation

In this sentence, o pacote do atum sounds like a particular package being discussed, not just any tuna package.

Mas means but.

It introduces a contrast:

• the tuna package is open
• but the grape package is still closed

This is a very common conjunction in Portuguese.

Yes. That is completely normal.

• diz = says / is saying
• ficou = ended up / became / was left
• está = is

The reporting verb can be in the present, while the content of what is reported includes past and present information.

So the structure is:

• Pedro says
  
  • the tuna package ended up open
  • but the grape one is still closed

This mixture of tenses is natural in both Portuguese and English.

It is better to think of o here as a nominal substitute: it replaces the noun pacote that was already mentioned.

So instead of repeating:

• o pacote do atum ... mas o pacote das uvas...

Portuguese uses:

• o pacote do atum ... mas o das uvas...

English does something similar with the one:

• the tuna package, but the grape one...

So yes, it has a pronoun-like function, but the key idea is that it stands in for an omitted noun.