Learn Hardcore Russian: Я точно закрыл дверь.

While точно can mean "exactly" in contexts like точно так (exactly like that), in Я точно закрыл дверь it conveys certainty—"I definitely closed the door."

Why is закрыл used instead of закрывал?

закрыл is the perfective past tense of закрыть, indicating a completed action ("I closed it and now it's closed"). закрывал is imperfective, used for ongoing or habitual actions ("I was closing the door" or "I used to close the door regularly").

Why is дверь in the accusative case?

In Russian, direct objects of transitive verbs take the accusative case. дверь is feminine, and its accusative form (the object form) happens to look the same as the nominative: дверь.

How would a female speaker say this sentence?

Russian past-tense verbs agree in gender. A male speaker uses закрыл, while a female would say закрыла: Я точно закрыла дверь.

Why is there no article like "the" or "a" before дверь?

Russian has no articles. Definiteness (the) or indefiniteness (a) is understood from context. Here it's clear from the situation that it's "the door."

Can we change the word order? For instance, Точно я закрыл дверь?

Russian word order is flexible but changes emphasis. Я точно закрыл дверь (neutral), Точно я закрыл дверь emphasizes that it's you who definitely closed it. Placing точно after the verb (Я закрыл точно дверь) sounds unnatural.

How do you pronounce закрыл дверь and where is the stress?

закрыл is pronounced za-KRYL (stress on the second syllable), дверь is DVER' (stress on the only vowel). Together: za-KRYL DVER'.

Could I use another adverb like уверенно or обязательно instead of точно, and what's the difference?

You can swap in different adverbs, but the nuance shifts. уверенно ("confidently") describes the manner of action, not your certainty about having done it. Я уверенно закрыл дверь would sound odd if you mean "I am sure I closed it." обязательно ("certainly"/"without fail") often implies obligation or future certainty ("I will definitely"). So Я точно закрыл дверь is the most natural way to express that you are sure you closed the door.