A declaração anual está pronta.

A is the feminine singular definite article, meaning the.

So A declaração anual = the annual declaration/report.

It appears because declaração is a feminine singular noun. In Portuguese, articles usually match the noun’s gender and number:

• o = masculine singular
• a = feminine singular
• os = masculine plural
• as = feminine plural

Portuguese uses articles more often than English does, so keeping a here sounds natural.

In Portuguese, every noun has grammatical gender, and declaração is feminine.

A very common clue is the ending -ção, which is almost always feminine:

• a declaração
• a informação
• a situação
• a tradução

So even though the word does not end in -a, it is still feminine.

Because pronta is an adjective describing declaração, and adjectives usually agree with the noun in gender and number.

Since declaração is feminine singular, the adjective must also be feminine singular:

• a declaração está pronta = feminine singular
• o documento está pronto = masculine singular
• as declarações estão prontas = feminine plural
• os documentos estão prontos = masculine plural

So pronta matches declaração.

Portuguese uses estar for states or conditions, and ser for more essential or permanent characteristics.

Here, pronta means ready, which is a condition or status, so estar is the natural choice:

• A declaração anual está pronta. = The annual declaration is ready.
• A declaração anual é importante. = The annual declaration is important.

So:

• está pronta = is ready, is in a ready state
• é pronta would sound wrong in this context

Here it functions as an adjective meaning ready.

Even though some forms in Portuguese can look like participles, pronto/pronta is very commonly used as an adjective:

• O jantar está pronto. = Dinner is ready.
• A resposta está pronta. = The answer is ready.

So in this sentence, it is simply describing the condition of the declaration.

In Portuguese, adjectives often come after the noun, especially when they are just describing it in a straightforward way.

So:

• declaração anual = annual declaration
• literally, declaration annual

This is normal word order in Portuguese. In some cases adjectives can come before the noun, but with a factual descriptive adjective like anual, the usual place is after the noun.

No. Anual does not change for masculine vs. feminine in the singular.

So you can say:

• o relatório anual
• a declaração anual

But it does change in the plural:

• os relatórios anuais
• as declarações anuais

So:

• singular: anual
• plural: anuais

A rough pronunciation for Brazilian Portuguese is:

deh-klah-rah-SOWN

A few key points:

• ção is very common in Portuguese and sounds roughly like sown, but with a nasal ending.
• The ã sound is nasal.
• The stress falls on the last syllable: decla-ra-ÇÃO

So the whole word is stressed at the end.

The accent marks mainly show stress and sometimes vowel quality.

• declaração: the ã shows a nasal vowel, and the word is stressed on the last syllable.
• está: the acute accent on á shows that the stress falls there: es-TÁ

Accents are important in Portuguese because they help you know how to pronounce the word correctly.

In normal Portuguese, that would usually sound unnatural.

The most natural sentence is:

• A declaração anual está pronta.

Portuguese generally likes to use the definite article in cases like this when talking about a specific thing. Omitting it might be possible in very special contexts, such as headlines, labels, or note-taking, but not in ordinary speech.

It would become:

As declarações anuais estão prontas.

Here is what changes:

• A → As
• declaração → declarações
• anual → anuais
• está → estão
• pronta → prontas

Everything agrees in number, and the adjective still agrees with the noun.