Η φόρμα είναι έτοιμη, αλλά χρειάζεται ακόμα η υπογραφή σου.

Because it agrees with η φόρμα, which is a feminine noun.

In Greek, adjectives change form to match the noun’s:

• gender
• number
• case

So here:

• ο έτοιμος = masculine
• η έτοιμη = feminine
• το έτοιμο = neuter

Since φόρμα is feminine, Greek uses έτοιμη.

Here φόρμα means a form in the sense of a document or paperwork.

This word can also mean other things depending on context, such as:

• uniform / outfit
• form / shape
• sometimes even physical condition in certain contexts

But because the sentence mentions a signature, the document meaning is clearly the right one here.

This is one of the most important grammar points in the sentence.

Here, η υπογραφή σου is in the nominative, not the accusative, because it is functioning as the subject of χρειάζεται.

So the structure is closer to:

• your signature is still needed

rather than:

• it still needs your signature

That is why Greek uses:

• η υπογραφή σου = nominative

and not:

• την υπογραφή σου = accusative

If you wanted to say but it still needs your signature, with the subject understood to be the form, Greek would normally use:

• αλλά χρειάζεται ακόμα την υπογραφή σου

So the article tells you a lot here.

In this sentence, it means something like is needed.

Greek χρειάζομαι / χρειάζεται can be used in a way that English speakers often experience as a bit different. In context:

• χρειάζεται η υπογραφή σου = your signature is needed

But Greek can also use χρειάζεται in the more straightforward needs sense when it takes an accusative object:

• Η φόρμα χρειάζεται την υπογραφή σου = The form needs your signature

So the form of the noun after the verb helps you understand which meaning is intended.

Because Greek weak possessive pronouns usually come after the noun.

So:

• η υπογραφή σου = your signature
• το βιβλίο μου = my book
• η φίλη του = his friend

This is completely normal Greek word order. English puts the possessive before the noun, but Greek usually puts these short possessive forms after it.

Here ακόμα means still or yet.

It shows that the situation is not complete yet:

• the form is ready
• but the signature has not been provided yet

So it adds the idea of something that remains to be done.

In many contexts, ακόμα can also mean even or any more, but here still / yet is the right sense.

Greek uses the definite article much more often than English does.

Here:

• Η φόρμα refers to a specific form already known in the situation
• η υπογραφή σου refers to the specific signature that is required

In Greek, articles are very commonly used with nouns that English might sometimes leave bare. In this sentence, omitting them would sound unnatural.

Also, the article helps show the grammatical role of the noun:

• η υπογραφή = nominative
• την υπογραφή = accusative

So the article is doing important grammatical work too.

Yes. Greek word order is more flexible than English word order.

This sentence is natural as written:

• Η φόρμα είναι έτοιμη, αλλά χρειάζεται ακόμα η υπογραφή σου.

But Greek could also shift things around for emphasis, for example:

• Η φόρμα είναι έτοιμη, αλλά ακόμα χρειάζεται η υπογραφή σου.
• Η φόρμα είναι έτοιμη, αλλά η υπογραφή σου χρειάζεται ακόμα.

Not every variant sounds equally natural in every context, but Greek allows more movement because endings and articles carry grammatical information.

The original version is a very natural, neutral way to say it.

Because αλλά means but, and here it connects two full clauses:

• Η φόρμα είναι έτοιμη
• αλλά χρειάζεται ακόμα η υπογραφή σου

In Greek, as in English, a comma is normally used before αλλά when it joins two clauses like this.

Yes, a little.

• Η φόρμα χρειάζεται την υπογραφή σου = more direct, more literal: The form needs your signature
• Χρειάζεται ακόμα η υπογραφή σου = slightly more impersonal or formal-sounding: Your signature is still needed

Both are correct, but the version in your sentence sounds a bit smoother and more natural in formal or administrative contexts. That makes sense, since the topic is a form and a signature.