Нужно позаботиться о документах.

Here нужно means it is necessary, it is needed, or more naturally in English, need to.

So the pattern is:

нужно + infinitive = it is necessary to do something

In this sentence:

Нужно позаботиться о документах = It’s necessary to take care of the documents / We need to take care of the documents

Because this is an impersonal construction. Russian often leaves the doer unspecified when the important idea is simply that something must be done.

So Нужно позаботиться о документах does not say exactly who must do it. Depending on context, it could mean:

• I need to take care of the documents
• We need to take care of the documents
• Someone needs to take care of the documents

If you want to say who needs to do it, you can add a dative pronoun or noun:

• Мне нужно позаботиться о документах = I need to take care of the documents
• Нам нужно позаботиться о документах = We need to take care of the documents
• Ему нужно позаботиться о документах = He needs to take care of the documents

After нужно, Russian normally uses the infinitive to say what action is necessary.

So the structure is:

• нужно сделать
• нужно идти
• нужно позаботиться

This is very similar to English need to do, where do also stays in its basic form.

This is a question of aspect.

• заботиться = imperfective
• позаботиться = perfective

In this sentence, позаботиться is used because the speaker means take care of this matter / make sure it gets done, as a complete action.

Compare:

• Нужно заботиться о здоровье.
  = One needs to take care of one’s health.
  This is general, ongoing, habitual.

• Нужно позаботиться о документах.
  = We need to take care of the documents.
  This is a specific task that should be handled.

So the perfective verb fits the idea of a concrete thing that needs to be dealt with.

Usually it is more practical here.

позаботиться о документах often means something like:

• make sure the documents are ready
• organize them
• check them
• submit them
• handle them properly

So it is often closer to take care of the documents or see to the documents than to emotional caring.

Because the verb заботиться / позаботиться requires the preposition о.

The pattern is:

заботиться о ком? о чём?
позаботиться о ком? о чём?

So the object of this verb is not used directly. It must appear with о.

Examples:

• заботиться о детях = to take care of the children
• позаботиться о семье = to take care of the family
• позаботиться о документах = to take care of the documents

This is just the normal government pattern of the verb.

It is the prepositional case, plural.

The preposition о in this expression takes the prepositional:

• о документе = about / concerning / taking care of the document
• о документах = about / concerning / taking care of the documents

So:

• singular: документ → о документе
• plural: документы → о документах

The ending -ах is a common prepositional plural ending for many nouns.

Not literally in normal English.

Although о often means about, in the expression заботиться о / позаботиться о, the whole phrase means to take care of or to look after / see to.

So:

• думать о документах = to think about the documents
• говорить о документах = to talk about the documents
• позаботиться о документах = to take care of the documents

Same preposition, but different verb = different overall meaning.

Yes. Russian word order is flexible.

The sentence as given:

Нужно позаботиться о документах

is neutral and natural.

You can also say:

О документах нужно позаботиться.

This puts more emphasis on о документах — as if you are highlighting the documents specifically.

Both are correct. The difference is mostly one of emphasis, not basic meaning.

Yes. In many contexts, надо and нужно are very close.

So:

• Нужно позаботиться о документах
• Надо позаботиться о документах

Both mean roughly We need to take care of the documents.

Very broadly:

• надо can sound a bit more conversational
• нужно can sound a bit more neutral or slightly more formal

But in everyday speech, both are extremely common.