Learn Turkish: Bu önemli belgeyi imzaladınız mı? - Did you sign this important document?

The root verb is imzala (to sign). We add the past tense suffix -dı (following vowel harmony with the 'a' in imzala), and finally the personal ending -nız for "you" (plural or formal singular).

Why is the question particle mı used here, and why is it a separate word?

In the past tense, you make a yes/no question by putting the question particle after the fully conjugated verb. It is always written with a space before it, but it still follows vowel harmony with the verb's last vowel. Because imzaladınız ends with an undotted 'ı', the particle becomes mı.

Why does the word for document (belge) have -yi at the end?

Because it is the specific thing being signed. When a specific noun is the direct object of a verb, it gets the accusative case ending. Belge ends in a vowel, so we need the buffer letter y before adding the suffix -i, making it belgeyi.

Does the word order for Bu önemli belgeyi work exactly like English?

Yes! Just like in English where we say "This important document", Turkish keeps the same order: demonstrative word (Bu), then adjective (önemli), and then the noun (belgeyi).