Regnskapsføreren kontrollerer bilaget.

Because -en is the definite article attached to the noun. In Norwegian, instead of usually putting a separate word like the before the noun, you often add the definite ending to the noun itself.

• regnskapsfører = accountant / bookkeeper
• regnskapsføreren = the accountant / the bookkeeper

This is very common in Norwegian:

• en bil = a car
• bilen = the car

So regnskapsføreren means the accountant.

Because bilag is a neuter noun in Norwegian.

Norwegian nouns have grammatical gender, and that affects the article endings:

• en noun (common gender) → definite singular usually ends in -en
• et noun (neuter) → definite singular usually ends in -et

So:

• et bilag = a voucher / supporting document / receipt-like accounting document
• bilaget = the voucher / the document

That is why the two nouns in the sentence have different endings:

• regnskapsføreren = the accountant
• bilaget = the document

Kontrollerer is the present tense form of the verb å kontrollere (to check / to inspect / to verify).

So:

• å kontrollere = to check
• kontrollerer = checks / is checking

In simple sentences like this, Norwegian present tense often covers both English meanings:

• The accountant checks the document
• The accountant is checking the document

Both can match Regnskapsføreren kontrollerer bilaget depending on context.

Because Norwegian usually puts definiteness on the noun itself.

English:

• the accountant
• the document

Norwegian:

• regnskapsføreren
• bilaget

So the idea of the is built into the endings -en and -et.

A separate definite word can appear in some situations, especially with adjectives:

• regnskapsføreren = the accountant
• den erfarne regnskapsføreren = the experienced accountant

But in your sentence, no separate definite word is needed.

Yes. This sentence uses the very common Subject – Verb – Object pattern:

• Regnskapsføreren = subject
• kontrollerer = verb
• bilaget = object

So it matches English very closely:

• The accountant checks the document.

This makes the sentence straightforward for English speakers.

In everyday translation, bilag can be tricky because it often has a more specific accounting meaning than plain English document.

Depending on context, bilag can mean something like:

• voucher
• supporting document
• receipt
• accounting document
• attachment (in some contexts)

In accounting, it usually refers to the documentation that supports a transaction. So in this sentence, bilaget is probably not just any random document, but a financial record or supporting piece of paperwork.

Yes. Norwegian very often forms long compound nouns by joining words together.

regnskapsfører is made from:

• regnskap = accounts / accounting
• fører = leader / keeper / one who manages

Together, regnskapsfører means accountant / bookkeeper, especially someone who handles bookkeeping or accounting records.

Compound nouns are extremely common in Norwegian, so it is useful to get used to reading them as smaller parts.

Yes, but the meaning changes.

• bilaget = the document / the voucher
  → a specific one, already known from the context

• et bilag = a document / a voucher
  → one document, not previously identified

So:

• Regnskapsføreren kontrollerer bilaget = The accountant checks the document
• Regnskapsføreren kontrollerer et bilag = The accountant checks a document

The difference is the same basic definite/indefinite distinction as in English.

A careful learner-friendly pronunciation guide could be written roughly like this:

Regnskapsføreren kontrollerer bilaget
≈ RAYNG-skahps-fuh-reh-ren kun-TROH-leh-rehr bee-LAH-guh

A few useful points:

• å / o-like vowels can vary by dialect and speaker.
• The r is often tapped or rolled lightly, depending on dialect.
• The g in bilaget is pronounced.
• Norwegian sentence stress usually falls on the main content words, especially regnskapsføreren, kontrollerer, and bilaget.

If you are learning Bokmål pronunciation, remember that actual pronunciation can vary quite a lot across Norway.

Because modern Norwegian has very little case marking on nouns. In a sentence like this, you understand who is doing what mainly from word order, not from special case endings.

So:

• Regnskapsføreren kontrollerer bilaget = the accountant checks the document

If you switched the nouns around, the meaning would change because the first noun is understood as the subject in this normal sentence pattern.

This is one reason Norwegian syntax can feel relatively accessible to English speakers.