Se cumprires o prazo, o chefe ficará contente.

In Portuguese, conditional clauses referring to the future require the future subjunctive after se.
• Se cumprires is the 2nd-person singular future subjunctive of cumprir.
• Se vais cumprir (periphrastic future) and Se cumprirás (future indicative) are not used in se-clauses.
Correct pattern: se + future subjunctive, then main clause in future indicative.

The future subjunctive is a verb form used after certain conjunctions—especially se, quando, logo que—whenever you talk about a future possibility or condition. It expresses “if/when something happens.”
Example:
• Quando chegares, avisar-me-ás. (When you arrive, you’ll let me know.)
• Se cumprires o prazo, o chefe ficará contente.

Portuguese is a pro-drop language: subject pronouns are optional because the verb ending already indicates person and number.
• Se (tu) cumprires o prazo is correct, but tu is usually omitted unless you want extra emphasis or contrast.

Prazo means deadline or time limit. In Portuguese, you normally refer to the deadline, so you include the definite article o.
• cumprir o prazo = “to meet the deadline.”
• Omitting o (e.g. cumprir prazo) sounds unnatural in this context.

Standard word order in Portuguese is Subject–Verb–Complement:
• O chefe (subject) + ficará (verb) + contente (adjective).
You can invert it for emphasis or a more literary feel:
• Ficará contente o chefe.
But in neutral or spoken language, o chefe ficará contente is preferred.

Both mean “will be pleased,” but they differ in style:
• ficará contente uses the simple future indicative (more formal or written).
• vai ficar contente uses the periphrastic future with ir (more common in speech).

Yes. All three are valid, but with slight nuance:
• contente: general happiness/satisfaction.
• satisfeito: emphasizes that expectations or requirements were met.
• feliz: strong or emotional happiness.
Choose based on the shade of meaning you want.

1. Take the 3rd-person plural of the preterite indicative: cumpriram.
2. Drop -am → stem cumprir-.
3. Add the future subjunctive endings:
   
   • eu cumprir
   • tu cumprires
   • ele/ela cumprir
   • nós cumprirmos
   • vós cumprirdes
   • eles/elas cumprirem