Hun sammenligner kopien med originalen, før hun lægger begge i mappen.

Because Danish usually puts the definite article at the end of the noun instead of using a separate word like the.

• en kopi = a copy
• kopien = the copy
• en original = an original
• originalen = the original
• en mappe = a folder
• mappen = the folder

The ending -en is the usual definite ending for singular common-gender nouns.

For the same reason: in Danish, the is often built into the noun itself.

So English says:

• the copy
• the original
• the folder

But Danish says:

• kopien
• originalen
• mappen

A separate word like den is usually used when there is an adjective:

• den gamle mappe = the old folder

But with a plain noun on its own, Danish normally just uses the ending.

Because Danish main clauses follow the V2 rule: the finite verb comes in the second position.

If the subject comes first, the order is:

• Hun sammenligner kopien med originalen.

Here, Hun is in first position, so sammenligner comes second.

If something else were placed first, then the subject would move after the verb:

• Før hun lægger begge i mappen, sammenligner hun kopien med originalen.

So Hun sammenligner ... is the normal word order when hun starts the main clause.

Because før introduces a subordinate clause, and subordinate clauses in Danish normally use subject + verb order.

So:

• før hun lægger begge i mappen = before she puts both in the folder

This is different from a main clause, where inversion can happen because of the V2 rule.

A useful contrast:

• Main clause: Nu lægger hun begge i mappen.
• Subordinate clause: ... før hun lægger begge i mappen.

Because the part after før is a full clause of its own, and it needs its own subject.

So the sentence contains two clauses:

• Hun sammenligner kopien med originalen
• før hun lægger begge i mappen

In English, you also usually repeat the subject:

• She compares the copy with the original before she puts both in the folder.

So Danish is working very similarly here.

Because the normal Danish pattern is:

• sammenligne A med B = compare A with B

So here:

• Hun sammenligner kopien med originalen

That is the standard way to say that one thing is being compared with another.

Here før means before, and it is a conjunction because it introduces a clause:

• før hun lægger begge i mappen

If før were followed just by a noun phrase, it would function more like a preposition:

• før mødet = before the meeting

So in this sentence, it is specifically a conjunction.

Begge means both.

Here it stands on its own as a pronoun and refers back to kopien and originalen:

• hun lægger begge i mappen = she puts both in the folder

Danish can often use begge by itself when the reference is clear.

You may also hear:

• hun lægger dem begge i mappen

That is also possible, but begge alone is perfectly natural here.

Because Danish often prefers a more specific placement verb where English simply says put.

Lægge is commonly used when something is laid down or placed, especially flat objects like papers. Since a copy and an original are likely sheets of paper, lægger is very natural.

Compare:

• lægge = lay/place
• sætte = set, often upright
• stille = place standing
• putte = put/stick into

So in this context, lægger is the idiomatic choice.

Because i means in or into, and a folder is treated as something you place papers inside.

So:

• i mappen = in the folder / into the folder

Danish often uses i with verbs of movement when the context already makes the direction clear.

You could sometimes say ind i mappen for extra emphasis on movement inward, but plain i mappen is the normal, natural wording here.

Because før hun lægger begge i mappen is a subordinate clause, and Danish often places a comma before such clauses.

In modern Danish, this comma is often optional, depending on the comma style being used. So both of these can be acceptable:

• Hun sammenligner kopien med originalen, før hun lægger begge i mappen.
• Hun sammenligner kopien med originalen før hun lægger begge i mappen.

The version with the comma is very common and very clear.

Because Danish often uses the present tense for:

• habitual actions
• instructions
• general procedures
• sequences that are clear from context

So this sentence can sound like a normal description of what she does as part of a routine:

• first she compares them
• then she puts both in the folder

English can do something similar too, especially in descriptions of routine: She compares the copy with the original before she puts both in the folder.