Learn Dutch: Het fruit wordt rot. - The fruit is becoming rotten.

In Dutch, worden is used as a linking verb meaning 'to become' or 'to get' when describing a change in state. If you said Het fruit is rot, it would mean the fruit is already rotten. Using wordt shows that the process is happening right now.

How would I say 'The fruit has become rotten' in the perfect tense?

You would say Het fruit is rot geworden. Remember from this lesson that worden uses zijn (to be) as its helping verb to form the perfect tense, and its past participle is geworden.

Why doesn't the adjective rot get an -e added to the end?

Adjectives usually only get an -e ending when they are placed directly before the noun they describe (for example, het rotte fruit). Because rot comes after the verb here, it stays in its basic, uninflected form.

Is the -dt in wordt pronounced differently than the -d in word?

No, they are pronounced exactly the same. The -dt ending sounds just like a regular 't'. The t is added purely for spelling rules because the subject, het fruit, is third-person singular ('it').