Billettkvitteringen dokumenterer reisen.

Because Norwegian usually writes compound nouns as a single word.

Here, Billettkvitteringen is built from:

• billett = ticket
• kvittering = receipt

So:

• billettkvittering = ticket receipt
• billettkvitteringen = the ticket receipt

English often uses separate words where Norwegian prefers one compound word.

The ending -en marks the noun as definite singular, so it works like the in English.

Compare:

• billettkvittering = a ticket receipt / ticket receipt
• billettkvitteringen = the ticket receipt

In Norwegian, definiteness is often shown by adding an ending to the noun instead of using a separate word.

Because Norwegian often puts the onto the end of the noun.

So instead of a separate word like English the receipt, Norwegian often says:

• kvitteringen = the receipt
• reisen = the journey / the trip

This is very normal in Norwegian.
If there is an adjective, you often get a separate determiner as well, for example:

• den gyldige billettkvitteringen = the valid ticket receipt

Dokumenterer is the present tense of å dokumentere.

So:

• å dokumentere = to document
• dokumenterer = documents / is documenting / serves as documentation for

A useful thing for English speakers: Norwegian verbs do not change for person.

So you get:

• jeg dokumenterer
• du dokumenterer
• han/hun dokumenterer

The verb form stays the same.

Reisen means the journey or the trip, not just journey/trip in general.

That suggests a specific journey is meant — for example, the journey connected with that ticket receipt.

Compare:

• reise = journey / trip
• en reise = a journey / a trip
• reisen = the journey / the trip

So the sentence is talking about a particular trip, not travel in general.

Yes, in Bokmål that is possible.

The noun reise is often treated as a feminine noun, and many feminine nouns in Bokmål can appear in two definite forms:

• reisen
• reisa

Both can mean the journey / the trip.

In practice:

• reisen is very common in neutral Bokmål
• reisa can sound more traditional, more distinctly feminine, or more dialect-colored depending on context

So reisen in your sentence is completely normal.

It follows the standard subject–verb–object pattern:

• Billettkvitteringen = subject
• dokumenterer = verb
• reisen = object

So the structure is very similar to English:

• The ticket receipt documents the journey

This is one reason the sentence may feel fairly straightforward to an English speaker.

Not necessarily. Depending on context, dokumenterer can mean:

• documents
• proves
• serves as documentation for
• shows evidence of

In this sentence, it likely means something like:

• the ticket receipt serves as proof of the journey

So the exact English wording can vary slightly even though the Norwegian verb stays the same.

It is capitalized only because it is the first word of the sentence.

Unlike German, Norwegian does not capitalize all nouns.

So in the middle of a sentence, it would normally be lowercase:

• Jeg fant billettkvitteringen. = I found the ticket receipt.

If you wanted an indefinite version, you could make the nouns indefinite, for example:

• En billettkvittering dokumenterer en reise.

That means something like A ticket receipt documents a journey.

However, this sounds more general and less natural in many real-life situations. The original sentence with billettkvitteringen and reisen sounds like it refers to a specific receipt and a specific trip, which is often what you want.