Learn Hardcore Dutch: Anna bewaart de notitie in haar map.

Proper nouns in Dutch (like Anna) typically don’t take an article. You’d only use an article in very specific cases (e.g. nicknames or set expressions), but for a person’s name you just say Anna, not de Anna or een Anna.

Why does the verb bewaart appear directly after Anna?

In a Dutch main clause the finite verb must occupy the second position (V2 word order). Here the subject Anna is first, so the conjugated verb bewaart comes second. Everything else (object, adverbials, etc.) follows.

Why is the definite article de used before notitie but omitted before map?

When you use a possessive pronoun (like haar), you don’t add another article before that noun. So it’s de notitie (the note) but haar map (her folder), not haar de map. If you wanted to say “the folder” without possession, you’d say de map.

Why do we use haar instead of zijn?

haar is the third-person singular feminine possessive pronoun (“her”). zijn is the third-person singular masculine possessive (“his”). Since Anna is female, we say haar map.

Why is the preposition in used? Could we not use op or aan?

in indicates that something goes inside a container (the folder). op would mean “on top of” (the note sits on the folder), and aan would mean “to” or “on” in a different sense (“attached to”). To express “inside her folder,” Dutch uses in.

Can we change the word order, for example by starting with the prepositional phrase?

Yes. If you front the PP, you must keep the finite verb in second position. For example:
In haar map bewaart Anna de notitie.
Here In haar map is first, bewaart remains second, and the subject Anna moves to third.