Jeg underretter kortudstederen, spærrer kortet og vedlægger dokumentationen.

Because all three verbs share the same subject.

In Danish, just like in English, you do not need to repeat the subject when one person does several actions in a row:

Jeg underretter kortudstederen, spærrer kortet og vedlægger dokumentationen.

That works like:

I notify the card issuer, block the card, and attach the documentation.

Repeating jeg each time would sound unnecessary: Jeg underretter ..., jeg spærrer ..., og jeg vedlægger ...

That version is possible, but much less natural here.

Underretter is the present tense of the verb at underrette.

So:

• at underrette = to notify / to inform
• jeg underretter = I notify / I am notifying

In Danish, the present tense often ends in -r:

• at spærre → spærrer
• at vedlægge → vedlægger

In a sentence like this, the present tense can sound a bit like a formal statement of what the speaker is now doing: I hereby notify..., block..., and attach...

Because underrette can take a direct object for the person or organization being informed.

So Danish works like this:

• at underrette nogen = to notify someone
• at underrette nogen om noget = to notify someone about something

Here, only the recipient is mentioned:

Jeg underretter kortudstederen
= I notify the card issuer

If you wanted to add what you are notifying them about, you would use om:

• Jeg underretter kortudstederen om tyveriet.
• I notify the card issuer about the theft.

Yes. Danish very often forms compound nouns as a single word.

kortudstederen is built from:

• kort = card
• udsteder = issuer
• -en = the (definite ending)

So literally it is: card-issuer-the

This is completely normal in Danish. The same thing happens in many other compounds:

• sygesikring = health insurance
• kreditkortnummer = credit card number
• pasnummer = passport number

As a rule, Danish prefers writing these as one word, where English often uses two words.

Because Danish usually marks definiteness by adding an ending to the noun.

So:

• en kortudsteder = a card issuer

• kortudstederen = the card issuer

• et kort = a card

• kortet = the card

• en dokumentation = documentation
• dokumentationen = the documentation

This is one of the biggest differences from English. English usually puts the before the noun, but Danish often puts the definite marker at the end.

Because Danish nouns belong to different grammatical genders.

There are two main genders in modern Danish:

• common gender (en-words)
• neuter (et-words)

Examples from the sentence:

• et kort → kortet
• en udsteder → udstederen
• en dokumentation → dokumentationen

So the definite singular endings are usually:

• -en for common gender nouns
• -et for neuter nouns

That is why:

• kort becomes kortet
• kortudsteder becomes kortudstederen

In compounds, the last part decides the gender. Since udsteder is an en-word, kortudsteder is also an en-word.

Here spærrer kortet means something like block the card or have the card disabled so it can no longer be used.

The verb at spærre often means:

• to block
• to bar
• to disable access

With bank cards or credit cards, it means stopping the card from being used for payments or withdrawals.

So this is not about physically locking something. It is about making the card invalid in the system.

Yes, vedlægger is quite formal.

It comes from at vedlægge, which means:

• to attach
• to enclose

It is especially common in formal writing, emails, applications, insurance claims, and official documents.

Examples:

• Jeg vedlægger en kopi af kvitteringen.
  = I attach/enclose a copy of the receipt.
• Vedlagt finder du dokumentationen.
  = Attached you will find the documentation.

In everyday speech, people might choose a less formal wording depending on context, but vedlægge is very natural in written administrative Danish.

Because the sentence lists several actions, and the first two are separated without a conjunction.

Structure:

• Jeg underretter kortudstederen,
• spærrer kortet
• og vedlægger dokumentationen.

So the comma helps separate the first action from the next one. Then the last action is introduced by og = and.

In English, you would often write: I notify the card issuer, block the card, and attach the documentation.

So the Danish comma here is functioning as a list separator between coordinated actions.

Yes, it sounds fairly formal and administrative.

Words like:

• underretter
• vedlægger
• dokumentationen

are typical of official, legal, banking, or insurance language.

A more everyday version might use simpler wording, for example:

• Jeg giver kortudstederen besked, spærrer kortet og sender dokumentationen med.

That said, the original sentence is perfectly natural in a formal context such as a claim form, report, or written statement.

Yes. In context, it very likely means I am hereby doing these actions now.

Danish present tense is often used in formal statements to describe an action being carried out at the moment of writing:

• Jeg bekræfter ... = I confirm ...
• Jeg erklærer ... = I declare ...
• Jeg underretter ... = I notify ...

So this sentence does not just describe a habit or routine. It sounds like a formal declaration of immediate action.