Den uvedkommende åpnet dokumentet.

Because den uvedkommende is a definite noun phrase: it means a specific person, not just any person.

Here, uvedkommende is being used like a noun meaning something like the unauthorized person / the outsider / the person who wasn’t supposed to be involved. Norwegian often uses den with an adjective that stands in for a noun.

So:

• en uvedkommende = an unauthorized person / an outsider
• den uvedkommende = the unauthorized person / the outsider

It is basically an adjective used as a noun.

On its own, uvedkommende is an adjective that can mean things like:

• not involved
• unauthorized
• irrelevant
  depending on context.

In this sentence, it refers to a person, so it functions like a noun phrase: the unauthorized person or the outsider.

This is similar to English expressions like:

• the rich
• the poor
• the accused

Because the phrase refers to a person, and in this kind of usage Norwegian normally uses den for a singular person-like referent.

Very roughly:

• den = common gender singular
• det = neuter singular
• de = plural

Since den uvedkommende refers to one person, den is the natural choice.

Because adjectives ending in -ende usually keep the same form in Norwegian.

That means uvedkommende does not change for gender, number, or definiteness the way many other adjectives do.

Compare:

• en spennende bok
• et spennende spill
• de spennende kapitlene

The adjective spennende stays the same, and uvedkommende works the same way.

Here, åpnet is the preterite (simple past) of å åpne = to open.

So:

• å åpne = to open
• åpner = opens / is opening
• åpnet = opened

In this sentence, it is the main verb in the past tense: opened.

A useful extra point: åpnet can also be a past participle in other contexts, but here it is clearly the finite past-tense verb because it comes directly after the subject:

• Den uvedkommende åpnet dokumentet.

Because dokumentet is the definite singular form: the document.

The noun is:

• et dokument = a document
• dokumentet = the document

Norwegian usually marks definiteness by adding an ending to the noun, instead of using a separate word like English the.

So:

• et dokument = a document
• dokumentet = the document

Because Norwegian normally puts the definite meaning on the end of the noun.

So English uses:

• the document

But Norwegian uses:

• dokumentet

You only add an extra article like den/det/de in certain structures, especially when there is an adjective before a definite noun:

• det store dokumentet = the big document

In your sentence, there is no adjective before dokumentet, so dokumentet alone is enough.

No, this sentence has the basic subject–verb–object order:

• Den uvedkommende = subject
• åpnet = verb
• dokumentet = object

So it lines up neatly with English.

However, Norwegian is a V2 language, which means the finite verb normally comes in the second position in main clauses. In this sentence, that produces the same order as English because the subject comes first.

For example:

• I går åpnet den uvedkommende dokumentet.
  = Yesterday, the unauthorized person opened the document.

Notice that åpnet still stays in second position.

Yes. uvedkommende is quite context-dependent.

It can mean things like:

• irrelevant
• not involved
• unauthorized
• not concerned with the matter

In this sentence, because it refers to a person opening a document, the most natural meaning is something like an unauthorized person or someone who should not have had access.

So the exact English wording can change depending on context, even though the Norwegian word is the same.

It is understandable and correct, but it sounds a bit formal or official, almost like something from a report, warning, or legal/security context.

In more everyday speech, people might also say things like:

• en fremmed
• en person som ikke skulle være der
• en uvedkommende person

So den uvedkommende åpnet dokumentet sounds somewhat formal, but very plausible in the right context.

Yes. That would mean an unauthorized person / an outsider opened the document.

The difference is:

• en uvedkommende = an unspecified person
• den uvedkommende = a specific person already identifiable in the context

So the choice depends on whether the person is being introduced for the first time or is already known from the situation.