Грузоподъёмность указана в документе.

Because it is the subject of the sentence.

In Грузоподъёмность указана в документе, the thing being talked about is грузоподъёмность. Russian subjects normally appear in the nominative.

A rough grammatical breakdown is:

• грузоподъёмность — subject, nominative singular
• указана — predicate
• в документе — prepositional phrase meaning in the document

So this is structurally similar to:

• Информация указана в документе.
• Дата указана в письме.

Because it agrees with грузоподъёмность, which is feminine singular.

The word указана is the short form passive participle of указать / указать in the sense of stated / indicated / specified. In Russian, this short form changes for gender and number:

• masculine: указан
• feminine: указана
• neuter: указано
• plural: указаны

Since грузоподъёмность is a feminine noun, you get:

• Грузоподъёмность указана...

Compare:

• Адрес указан в документе. — masculine
• Дата указана в документе. — feminine
• Место указано в документе. — neuter
• Данные указаны в документе. — plural

It is best understood here as a short-form passive participle, which behaves a lot like part of the predicate.

For learners, the most practical way to think about it is:

• указана = is indicated / is stated / is specified

So in this sentence it functions very much like the English predicate is stated.

Its full form would be указанная, but the full form is usually used like an adjective before a noun, while the short form is commonly used as the predicate:

• указанная грузоподъёмность — the stated/specified load capacity
• грузоподъёмность указана — the load capacity is stated/specified

Because after в, Russian uses different cases depending on meaning:

• в + accusative = motion into
• в + prepositional = location in

Here there is no movement. The meaning is in the document, so Russian uses the prepositional case:

• документ → в документе

Compare:

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

So in this sentence, в документе is correct because it describes where the information appears.

It is a compound noun meaning something like load capacity, lifting capacity, or payload capacity, depending on context.

It is built from parts:

• груз — load, cargo
• подъём — lifting
• -ность — a suffix that makes an abstract noun, often like English -ness or -ity

So the word literally points to the idea of capacity for lifting/carrying a load.

This kind of long compound noun is common in technical Russian.

Yes, it is often written without ё in everyday Russian text, so you may also see:

• грузоподъемность

But the correct pronunciation and stress are clearer with ё:

• грузоподъёмность

That ё is always pronounced yo, even when many texts replace it with е.

For learners, it is very helpful to pay attention to ё, because it prevents pronunciation mistakes.

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

The neutral order here is:

• Грузоподъёмность указана в документе.

But you could also say:

• В документе указана грузоподъёмность.

This version puts a bit more emphasis on where it is stated.

In many cases both are grammatically correct, but the focus changes slightly. Russian often moves information around for emphasis, topic-focus structure, or style.

Because Russian often uses this kind of passive construction when the doer is not important, unknown, or obvious.

In English, this is similar to:

• The load capacity is stated in the document.

You do not need to say who stated it. The important point is that the information appears in the document.

If you wanted to name the agent, Russian would usually choose a different structure, for example an active sentence.

Not in this sentence.

Указано is neuter singular, but грузоподъёмность is feminine singular, so the forms must agree.

Correct:

• Грузоподъёмность указана в документе.

Incorrect:

• Грузоподъёмность указано в документе.

You would use указано with a neuter noun, for example:

• Место указано в документе.

Because Russian has no articles.

English distinguishes between:

• a document
• the document

Russian usually does not mark that difference with a separate word. Context tells you whether the meaning is more like a document, the document, or simply in documents in a broader sense.

So в документе can mean:

• in the document
• in a document

depending on context.

All three can work, depending on context.

The verb указывать / указать has a broad meaning range, and in official or technical writing указан(а) often means:

• stated
• indicated
• specified

So this sentence could naturally be translated in different ways, for example:

• The load capacity is stated in the document.
• The load capacity is indicated in the document.
• The load capacity is specified in the document.

In technical or bureaucratic Russian, this kind of wording is very common.