Полицейский проверил документы.

Yes, here полицейский is a noun meaning police officer or policeman.

It has an adjective-like form because historically it comes from an adjective, and it still declines like one. In this sentence it is masculine singular nominative, because it is the subject.

Related forms:

• полицейский = male police officer
• полицейская = female police officer
• полицейские = police officers

Проверил is past tense.

Russian past tense is often built with -л, so проверил means checked. In this sentence, it refers to a completed action in the past: the officer checked the documents.

In the Russian past tense, the verb agrees with the subject in gender and number.

Here the subject is полицейский, which is masculine singular, so the verb is проверил.

Compare:

• полицейский проверил = a male officer checked
• полицейская проверила = a female officer checked
• полицейские проверили = the officers checked

Unlike English, Russian past tense does not show person the same way; gender/number is important instead.

This is a question of aspect.

• проверил is perfective
• проверял is imperfective

Проверил presents the action as completed: the checking was done.

Проверял would suggest:

• an ongoing process,
• repeated checking,
• or background action depending on context.

So Полицейский проверил документы means the officer finished checking the documents.

Документы is in the accusative plural, because it is the direct object of the verb проверил.

The officer did the action, and the documents received the action, so they go in the accusative case.

Because документы is an inanimate plural noun.

In Russian, for inanimate plural nouns:

• nominative plural = accusative plural

So:

• nominative: документы
• accusative: документы

That is normal.

This is different from many animate nouns, where the accusative plural usually matches the genitive plural instead.

Russian does not have articles.

So Полицейский проверил документы can mean:

• The police officer checked the documents
• A police officer checked the documents

Context tells you which meaning is more natural.

Yes, Полицейский проверил документы is a very normal, neutral word order: subject + verb + object.

Russian word order is more flexible than English because case endings show grammatical roles. So other orders are possible, for example:

• Документы проверил полицейский = more emphasis on documents or on it was the officer who checked them
• Проверил документы полицейский = possible, but less neutral and more context-dependent

So the given order is the safest and most standard one for learners.

In this kind of context, документы often means official papers / identification documents, not just any random papers.

For example, it could mean things like:

• a passport
• ID
• driver's license
• registration papers

So проверить документы is a very common phrase meaning to check someone's papers/ID.

The stress is:

полице́йский провери́л докуме́нты

So the stressed syllables are:

• по-ли-це́й-ский
• про-ве-ри́л
• до-ку-ме́н-ты

Stress is important in Russian, because it is not always predictable and can change between forms.