De houder ondertekent het adoptiecontract.

Dutch nouns have grammatical gender/common article patterns, so you have to learn which article goes with each noun:

• de houder = the holder / owner / keeper
• het adoptiecontract = the adoption contract

There is not always a logical reason visible from the English translation. You usually need to memorize the article with the noun.

A useful clue here is that adoptiecontract is a compound noun, and in Dutch the last part usually determines the article. Since contract is a het-word, adoptiecontract is also a het-word.

Because the subject is de houder, which is third person singular: he/she/it.

The verb is ondertekenen = to sign. In the present tense:

• ik onderteken
• jij ondertekent / onderteken
• u ondertekent
• hij/zij/het ondertekent
• wij ondertekenen
• jullie ondertekenen
• zij ondertekenen

So in De houder ondertekent het adoptiecontract, the form ondertekent is the normal present-tense form for a singular subject.

Yes, in this sentence it is very similar to English:

• De houder = subject
• ondertekent = verb
• het adoptiecontract = object

So the pattern is:

Subject + verb + object

That said, Dutch word order changes more often than English in other sentence types. For example, if you begin with a time word or another element, the verb still stays in second position:

• Vandaag ondertekent de houder het adoptiecontract.
  = Today the holder signs the adoption contract.

Yes. Both can relate to signing, but ondertekenen is more specific and formal.

• tekenen can mean to draw or to sign
• ondertekenen specifically means to sign officially, especially a document

So with a formal document like a contract, ondertekenen is a very natural choice.

Because Dutch usually writes compound nouns as one single word.

So:

• adoptie
  • contract → adoptiecontract

This is very common in Dutch. English often uses separate words where Dutch prefers one compound word.

Other examples:

• ziekenhuis = hospital
• arbeidscontract = employment contract
• paspoortfoto = passport photo

Houder literally means holder, but in real usage it often means something more natural in English depending on the context, such as:

• owner
• keeper
• person in possession of something
• account holder
• license holder

So in an adoption-related context, houder might refer to the current owner or keeper, not necessarily someone who is physically “holding” something.

No. Ondertekenen is not a separable verb.

That means the prefix onder- stays attached to the verb:

• Ik onderteken het contract.
• Hij ondertekent het contract.
• Hij heeft het contract ondertekend.

Compare that with a separable verb like opbellen:

• Ik bel hem op.

That kind of splitting does not happen with ondertekenen.

You would usually change both the subject and the verb:

• De houders ondertekenen het adoptiecontract.
• The holders sign the adoption contract.

Changes:

• houder → houders
• ondertekent → ondertekenen

The object het adoptiecontract stays singular unless you also want to make that plural:

• De houders ondertekenen de adoptiecontracten.

A common past-tense version is:

• De houder ondertekende het adoptiecontract. = The holder signed the adoption contract.

You can also use the perfect tense:

• De houder heeft het adoptiecontract ondertekend. = The holder has signed the adoption contract.

Both are correct, but Dutch often uses the perfect tense in everyday speech more than English does.

A few pronunciation points that English speakers often notice:

• houder: the ou sounds somewhat like the vowel in English now
• ondertekent: the onder- begins with a short o, and tekent has a clear t at the end
• Dutch r can vary by region, so do not worry if you hear different versions

Roughly:

• houder ≈ HOW-der
• ondertekent ≈ ON-der-TAY-kent

These are only approximate English-style hints, but they can help at the start.

Normally no. In a full normal sentence like this, Dutch usually needs the article:

• De houder ondertekent het adoptiecontract.

Without the articles, it sounds unnatural unless you are speaking in a special style such as notes, labels, or headlines.

Dutch uses articles very regularly, just as English does with the and a/an.