El acta ya está firmada.

Because acta is a feminine noun that begins with a stressed a- sound. In Spanish, singular feminine nouns of this type usually take el instead of la for ease of pronunciation.

So:

• el acta
• el agua
• el alma

But the noun is still feminine, which is why the adjective is feminine:

• El acta ya está firmada.

In the plural, it goes back to las:

• las actas

It is feminine.

A good way to tell is by the agreement:

• el acta firmada
• esta acta
• las actas

The article el here does not make the noun masculine. It is just a special article choice used before certain feminine nouns in the singular.

Because firmada agrees with acta, which is feminine singular.

Past participles used this way in Spanish often behave like adjectives, so they must match the noun in gender and number:

• el acta firmada — feminine singular
• los documentos firmados — masculine plural
• las cartas firmadas — feminine plural

So firmada is correct because it refers to acta.

Because estar + past participle usually describes the resulting state of something.

So está firmada means the document is now in a signed state: it has been signed already.

By contrast, ser + past participle is the standard passive and focuses more on the action itself:

• El acta fue firmada por la directora. — The record was signed by the director.

In this sentence, the important idea is the current status, not who signed it, so está firmada is the natural choice.

Not exactly in the same way as English is signed can be.

In Spanish, estar + participle is usually called a resultative construction. It describes the condition something is in after an action.

• El acta ya está firmada. — The record is already signed / has already been signed.

If you want a more action-focused passive, Spanish often uses:

• ser + participle: El acta fue firmada...
• or se constructions: El acta ya se ha firmado.

So this sentence is more about the state of the document than the signing event itself.

Ya means already here.

It tells you that the signing has happened by now, often with one of these possible tones:

• reassurance: it is done
• update: this step is complete
• impatience or urgency, depending on context

Compare:

• El acta está firmada. — The record is signed.
• El acta ya está firmada. — The record is already signed.

So ya adds the idea of completion relative to some expectation or timeline.

Yes.

• El acta está firmada. is perfectly correct.

Without ya, the sentence simply states the condition. With ya, it emphasizes that this condition has been reached already.

So the difference is not grammar, but nuance.

Yes, and it is a natural alternative, but the focus changes slightly.

• El acta ya está firmada. — Focus on the current state: the document is signed.
• El acta ya se ha firmado. — Focus on the action having been completed: the document has been signed.

Both are common, but está firmada sounds more like a status update, while se ha firmado sounds more event-oriented.

Yes, if the context makes it clear what you are talking about.

For example, if both speakers already know the topic is the record or document, Ya está firmada is completely natural.

Notice that firmada still stays feminine singular because the omitted noun is still understood to be el acta.

The original order is the most neutral and natural:

• El acta ya está firmada.

You may also hear:

• El acta está ya firmada.

That version is possible, but slightly more marked or formal in tone.

If the context is very clear, Spanish may also move things around for emphasis, but for a learner, the original order is the safest and most natural choice.

It usually refers to an official written record or formal document.

Depending on context, it can mean things like:

• minutes of a meeting
• an official record
• a formal certificate or report

So it is not just any paper or document. It usually has an administrative, legal, or official sense.

You can add por plus the person or role, but in Spanish that is more common with an action-focused passive than with estar.

Natural options include:

• El acta fue firmada por la secretaria.
• La secretaria firmó el acta.

You can sometimes hear:

• El acta ya está firmada por la secretaria.

That is possible, but it still mainly emphasizes the document’s signed state rather than the signing event itself.