Четверо подписали документ.

Четверо is a collective numeral, while четыре is the ordinary cardinal numeral four.

In this sentence, четверо means a group of four people. Russian often uses collective numerals for:

• groups of males,
• mixed-gender groups,
• children,
• or when the people are referred to as a group rather than as separate individuals.

So Четверо подписали документ means Four people signed the document.

If you used четыре, you would normally need a noun after it, for example:

• четыре человека подписали документ
• четыре сотрудника подписали документ

Saying just четыре подписали документ would sound incomplete in normal Russian.

Not necessarily, but it often suggests a group that is:

• all male,
• mixed,
• or children.

It is not normally used for a group of adult women only. For adult women, Russian usually prefers the ordinary numeral plus a noun:

• четыре женщины подписали документ

So четверо подписали документ could mean:

• four men,
• a mixed group of four people,
• four children, depending on context.

Yes, you can think of an implied idea like four people.

Russian allows collective numerals like двое, трое, четверо to stand on their own when the noun is obvious or unimportant. So:

• Четверо подписали документ = Four people signed the document

English usually needs a noun such as people, but Russian does not have to state it here.

Because the subject is plural: четверо = four people.

Подписали is the past tense plural form of the verb подписать.

Compare:

• он подписал = he signed
• она подписала = she signed
• они подписали = they signed

Since четверо refers to more than one person, the verb must be plural:

• Четверо подписали документ

Подписали is:

• past tense
• perfective aspect

The infinitive is подписать.

The perfective aspect shows the action as completed. So подписали means they did sign / signed successfully / finished signing.

If you used the imperfective verb подписывать, the past plural form would be подписывали, which would give a different meaning, such as:

• they were signing,
• they used to sign,
• they signed repeatedly, depending on context.

So in this sentence, подписали presents the signing as a completed event.

Документ is in the accusative singular because it is the direct object of the verb подписали.

The verb подписать takes a direct object: you sign something.

For masculine inanimate nouns, the accusative singular looks the same as the nominative singular:

• nominative: документ
• accusative: документ

So although the form does not change, its function here is accusative.

Here четверо is in the nominative case because it is the subject of the sentence.

It answers the question who signed the document? — четверо.

Collective numerals do change by case in Russian, but in this sentence you are seeing the basic nominative form.

Yes. Russian word order is flexible, and changing it can shift the emphasis.

The neutral order here is:

• Четверо подписали документ.

Other possible orders include:

• Документ подписали четверо.
  This emphasizes the document or highlights the fact that four people signed it.
• Подписали документ четверо.
  This is less neutral and more context-dependent, but still possible.

So the basic meaning stays the same, but the focus changes.

The stress is:

• четвЕро
• подписАли
• докумЕнт

So the sentence is pronounced:

• четвЕро подписАли докумЕнт

Stress matters in Russian, so it is useful to learn the words with stress from the beginning.

In a basic translation, yes—but in English you usually need to make the hidden noun explicit.

So the natural translation is:

• Four people signed the document.

A word-for-word mapping like Four signed the document is possible in English, but it sounds less neutral and depends more on context. In Russian, четверо already carries the idea of four people as a group, so the sentence feels complete.