Срок действия указан в документе.

Literally, срок means term, period, or deadline, and действия comes from действие, meaning action, operation, or validity/functioning depending on context.

Together, срок действия is a fixed expression meaning period of validity, validity term, or expiration period. In documents, licenses, permits, contracts, and similar contexts, it usually means how long something remains valid.

So even though the literal parts may seem broad, the full phrase is best learned as one unit.

Because действия is in the genitive singular. Russian often uses this pattern:

срок + genitive

So:

• срок договора = the term of the contract
• срок аренды = the term of the lease
• срок действия = the period of validity

Here, действия depends on срок and answers the question срок чего? = the period of what? → of validity.

Указан is the short passive participle of the verb указать.

It agrees with срок, which is masculine singular, so the form is:

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

So:

• Срок указан = The term is indicated/stated
• Дата указана = The date is indicated/stated

This form is very common in formal and written Russian.

This is a very common point of confusion.

In Russian, a short passive participle like указан often describes a current state resulting from a completed action. So the idea is not just was indicated, but rather has been indicated and is now stated there.

That is why in English it is often translated as:

• is indicated
• is stated
• is specified

So although the Russian form is historically linked to a completed action, in context it often corresponds to present-time English.

Yes, but the meaning shifts a little.

• Срок действия указан в документе = The validity period is stated in the document.
  This focuses on the result: it is there, already written.

• Срок действия указывается в документе = The validity period is stated/is usually stated in the document.
  This sounds more like a general rule, procedure, or habitual practice.

So in a concrete statement about a particular document, указан is usually more natural.

Because в документе means in the document, that is, within its text or contents.

Russian often uses:

• в документе
• в статье
• в договоре
• в письме

when referring to information contained inside the text.

На документе would usually mean something physically on the document, such as a stamp, signature, mark, or note on the surface. So for written information as part of the content, в документе is the normal choice.

Документе is in the prepositional case.

The preposition в can take different cases:

• в + accusative = motion into something
  в документ would mean into the document in a very unusual/literal sense

• в + prepositional = location inside something
  в документе = in the document

Since this sentence describes where the information is located, Russian uses the prepositional case.

The word order can change. Russian word order is fairly flexible because the grammatical endings show the roles of the words.

For example:

• Срок действия указан в документе.
• В документе указан срок действия.

Both are correct.

The difference is mainly emphasis:

• Срок действия указан в документе starts with the topic the validity period
• В документе указан срок действия puts more focus on where it is stated

In many contexts, the second version may sound slightly more natural if the location is the new information.

Russian has no articles like a and the. So документ can mean:

• a document
• the document

depending on context.

In в документе, English may require in the document, but Russian simply uses the noun without an article. The listener understands whether it is definite or indefinite from the situation.

Not exactly.

• срок действия = period of validity
  Used for things like documents, visas, licenses, contracts, cards, subscriptions

• срок годности = shelf life / expiration date
  Used mainly for food, medicine, cosmetics, and other consumable products

So for a document, permit, or certificate, срок действия is the right phrase. Using срок годности there would sound wrong.

The sentence is passive, so the person or institution that wrote the information is not mentioned.

Russian often leaves the agent unstated when it is obvious, unknown, or unimportant. The focus here is on the fact that the validity period is written in the document, not on who wrote it.

If necessary, Russian could add the agent, but in official-style language it is very common not to mention it.