Таможенная пошлина указана в документе.

Because it agrees with пошлина, which is a feminine singular nominative noun.

• пошлина = a feminine noun
• таможенный = the dictionary form of the adjective, meaning customs
• feminine singular nominative form = таможенная

So таможенная пошлина means customs duty, with the adjective matching the noun in gender, number, and case.

Because it is the subject of the sentence.

In Таможенная пошлина указана в документе, the thing being talked about is the customs duty. That is why таможенная пошлина is in the nominative.

A rough grammatical breakdown is:

• Таможенная пошлина = subject
• указана = predicate
• в документе = location / where it is indicated

Указана is the short-form passive participle of указать.

In this sentence, it means something like:

• is indicated
• is stated
• is specified
• is listed

So the whole sentence has a passive meaning: the customs duty is indicated in the document.

This is a very common Russian pattern in formal or written language.

Because указана must agree with the subject, таможенная пошлина, which is feminine singular.

Compare:

• пошлина указана — feminine singular
• сбор указан — masculine singular
• условие указано — neuter singular
• данные указаны — plural

So the ending of the short-form participle changes to match the noun.

Because in Russian, the verb to be is usually omitted in the present tense.

English says:

• The customs duty is indicated in the document.

Russian simply says:

• Таможенная пошлина указана в документе.

This is completely normal. Russian does not usually use a present-tense equivalent of is/am/are in sentences like this.

Because в документе means in the document as a location, and after в with a location meaning, Russian uses the prepositional case.

• документ = dictionary form
• в документе = in the document

By contrast, в документ would suggest movement into the document, which does not fit here.

So:

• в документе = in the document
• в документ = into the document

Because Russian uses в when something is contained in the text or contents of a document.

• в документе = in the document, in its contents/text
• на документе = on the document, on its surface

So if you mean that the customs duty is mentioned as part of the document’s content, в документе is correct.

Yes, in meaning it is passive.

It does not say who indicated the customs duty. It focuses only on the result:

• the customs duty is indicated in the document

This is a very typical way to express passive meaning in Russian, especially in official, business, and legal language.

The underlying verb is указать — to indicate, to specify, to state.

The related forms are:

• указать — verb
• указанный — full passive participle, meaning indicated / specified
• указана — short-form feminine singular participle used as the predicate

For example:

• указанная в документе пошлина = the duty indicated in the document
• пошлина указана в документе = the duty is indicated in the document

So the full form acts more like an adjective before a noun, while the short form is commonly used in the predicate.

Yes, Russian word order is flexible.

The original sentence is neutral and natural:

• Таможенная пошлина указана в документе.

You could also say:

• В документе указана таможенная пошлина.

This version puts more emphasis on where it is indicated.

Both are correct, but the original is a straightforward neutral way to say it.

Yes, it sounds fairly formal or document-style.

Words like пошлина and structures like указана в документе are common in:

• legal language
• customs and trade contexts
• administrative writing
• official documents

In everyday casual speech, people might still say it, but it has a clearly official tone.