Learn German: Er ist wütend und zerreißt ein wichtiges Dokument. - He is angry and tears up an important document.

The base verb is reißen, which simply means "to pull" or "to tear." As this lesson covers, the prefix zer- adds the meaning of destruction or breaking something into pieces. By adding it to reißen, we get zerreißen, meaning "to tear up" or "to shred."

Will the prefix zer- ever split from the verb and go to the end of the sentence?

No, zer- is always an inseparable prefix. It stays glued to the verb no matter how the sentence is structured. Also, because it is inseparable, its past participle form doesn't take a ge- at the beginning (for example, "he has torn" is er hat zerrissen).

Why does the adjective wichtig get the ending -es here?

The phrase ein wichtiges Dokument is the direct object being torn up, so it is in the accusative case. Dokument is a neuter noun (das Dokument). Because the indefinite article ein has no special ending here to show the neuter gender, the adjective has to do the heavy lifting by taking the strong neuter ending -es.

Do I need to repeat the subject er after und?