Налогоплательщик подал справку о доходах.

Because it is the direct object of the verb подал.

The dictionary form is справка, but in this sentence it has to be in the accusative singular:

• справка = nominative singular
• справку = accusative singular

This happens because the sentence is saying that the taxpayer submitted what? — справку о доходах.

Since справка is a feminine inanimate noun ending in -а, its accusative singular changes -а to -у.

Налогоплательщик is the subject of the sentence, so it is in the nominative singular.

It is the person who performs the action:

• Налогоплательщик = the taxpayer
• подал = submitted/filed
• справку о доходах = an income certificate/statement

So this is the normal citation form of the noun.

In the past tense, Russian verbs agree with the subject in gender and number.

Here:

• подал = masculine singular
• подала = feminine singular
• подало = neuter singular
• подали = plural

Because the subject is налогоплательщик, which is grammatically masculine singular, the verb appears as подал.

The basic form is подать.

This is a perfective verb meaning to submit, file, hand in. In this sentence, подал means the action was completed: the taxpayer successfully submitted the document.

A useful pair is:

• подавать = imperfective
• подать = perfective

So:

• Налогоплательщик подавал справку can suggest process, repetition, or background context.
• Налогоплательщик подал справку means he submitted it, as a completed act.

After the preposition о, Russian normally uses the prepositional case.

So:

• доходы = nominative plural
• о доходах = prepositional plural

The phrase справка о доходах literally means a certificate about income/earnings, though in English we would usually translate it more naturally as income certificate, income statement, or proof of income, depending on context.

In Russian, documents of this type are very often described with доходы in the plural.

So справка о доходах is a standard bureaucratic expression meaning a document showing someone's income or earnings.

Even though English often uses singular income, Russian commonly uses plural доходы in this context. It sounds more natural and idiomatic in official language.

Yes, literally о means about or concerning.

So word-for-word, справка о доходах is something like a certificate about earnings/income.

But English usually does not phrase it that way. So the natural translation is something like:

• income certificate
• proof of income
• income statement

This is a good example of how Russian and English package the same idea differently.

Often yes, in official contexts, but not always exactly.

Справка is a very common Russian word for an official document confirming some fact. Depending on the situation, it can mean:

• certificate
• statement
• note
• confirmation
• record

So справка о доходах is an official document confirming income. In many cases certificate works well, but the best English translation depends on the real-world context.

Yes. Russian word order is more flexible than English because the cases show the grammatical roles.

The neutral order here is:

• Налогоплательщик подал справку о доходах.

But other orders are possible for emphasis, for example:

• Справку о доходах налогоплательщик подал.
• Подал налогоплательщик справку о доходах.

These are grammatical, but they sound different in emphasis or style. For a learner, the original order is the most neutral and natural.

Russian has no articles.

So налогоплательщик can mean:

• a taxpayer
• the taxpayer

and справку can mean:

• a certificate
• the certificate

Which one is meant depends on the context. English must choose an article, but Russian usually leaves that unstated unless something else makes it clear.

There are two main possibilities, depending on style.

A clearly feminine version would be:

• Налогоплательщица подала справку о доходах.

Here both the noun and the past-tense verb are feminine.

In some official or generic contexts, Russian may still use the masculine role noun more generally, but for learners, the clearest feminine form is:

• налогоплательщица
• подала

Yes, very normal.

In bureaucratic and administrative Russian, подать is commonly used with documents:

• подать заявление = submit an application
• подать декларацию = file a declaration/tax return
• подать справку = submit a certificate/document

So this sentence sounds natural and official. In this context, подал is often best understood as submitted or filed, not just gave.