Learn Hardcore Italian: Devo riscrivere il documento.

No. Italian normally drops subject pronouns because the verb ending shows the subject. Use io for emphasis or contrast: Io devo riscrivere il documento (I, not someone else, have to rewrite it).

Why is there no di before riscrivere?

Because dovere (like potere and volere) takes a bare infinitive. So you say devo riscrivere, not devo di riscrivere.

What does the prefix ri- add in riscrivere?

The prefix ri- means again/over, similar to English re-. Riscrivere typically implies doing the writing over, often more thoroughly, not just making small edits. You may also hear da capo (from scratch) for emphasis: Devo riscriverlo da capo.

Is riscrivere the same as scrivere di nuovo or rivedere?

scrivere di nuovo/nuovamente = write again (neutral paraphrase of riscrivere).
riscrivere = rewrite (often suggests a fuller redo).
rivedere/modificare = revise/edit (lighter changes). Don’t use rivedere if you mean a complete rewrite.

How do I replace il documento with a pronoun?

For a direct object pronoun:

Lo devo riscrivere = Devo riscriverlo (both are correct; second is more neutral/prosodically smooth). With two pronouns (rewrite it for him/her):
Glielo devo riscrivere = Devo riscriverglielo (gli/le + lo → glielo). This means “I have to rewrite it for him/her.”

How do I make it negative, and does non devo mean mustn’t or don’t have to?

Place non before the verb: Non devo riscrivere il documento.

In practice, non devo often means “I mustn’t/I’m not supposed to.”
To express “I don’t have to/It isn’t necessary,” prefer: Non è necessario che lo riscriva / Non c’è bisogno di riscriverlo / Non devo per forza riscriverlo. Context usually clarifies, but those paraphrases avoid ambiguity.

Why is it il documento and not lo documento? When would I use un documento?

il is the regular masculine singular article before most consonants: il documento.
lo is used before s + consonant (lo studente), z (lo zio), gn (lo gnocco), ps/pn (lo psicologo), x, y.
un documento means “a document” (not specific). Italian often uses the article with direct objects where English might omit it.

How do I talk about past or future necessity?

Past single/completed: Ho dovuto riscrivere il documento (I had to rewrite the document).
Ongoing/past background: Dovevo riscrivere il documento (I was supposed to/used to have to rewrite it).
Future: Dovrò riscrivere il documento (I will have to rewrite the document). If you want to say you actually did rewrite it: L’ho riscritto (I rewrote it).

What’s the past participle of riscrivere, and which auxiliary does it take?

Past participle: riscritto. It takes avere:

Ho riscritto il documento. With a preceding direct-object pronoun, the participle agrees in gender/number in careful/standard Italian:
L’ho riscritto (il documento, masc. sing.)
L’ho riscritta (la lettera, fem. sing.)
Li ho riscritti / Le ho riscritte (plural).

Any pronunciation tips for devo riscrivere?

devo: stress on the first syllable (DE-vo).
riscrivere: four syllables ri-SCRÌ-ve-re; the cluster scr is pronounced like “skr,” not “sh.” So “ri-SKRI-ve-re.”

Can the word order change for emphasis?

Yes. Italian allows topicalization and clitic doubling for focus:

Il documento, devo riscriverlo (Focus on “the document”).
Devo proprio riscrivere il documento (intensifies the obligation).
Lo devo riscrivere / Devo riscriverlo (both fine; initial lo can slightly emphasize the object).

Are there softer or alternative ways to express obligation?

dovrei riscrivere il documento = I should rewrite the document (softer).
È necessario/È opportuno riscrivere il documento.
Bisogna riscrivere il documento (impersonal “one/people must”).
Mi tocca riscrivere il documento (colloquial: I’m stuck having to).

Can riscrivere mean “to write to someone again”?

Yes, with an indirect object it means “to write again (to someone)”:

Ti riscrivo domani = I’ll write to you again tomorrow. In your sentence, with a direct object (il documento), it clearly means “rewrite.”