Ви заповните документ.

Ви can mean either:

• you when speaking to more than one person
• you when speaking to one person politely/formally

So this sentence could address:

• a group: You all will fill out the document
• one person formally: You will fill out the document

The informal singular pronoun would be ти.

In this sentence, Ви is capitalized simply because it is the first word of the sentence.

More generally, in Ukrainian writing, Ви with a capital letter can also be used as a polite form when addressing one person, especially in letters, emails, forms, and official communication. But in this sentence alone, the capital letter does not prove that it is formal singular, because sentence-initial words are capitalized anyway.

заповните is the 2nd person plural form of the verb заповнити.

With Ви, that means it matches either:

• you all will fill out
• you will fill out (formal singular)

Grammatically, it is a future tense form.

Because заповнити is a perfective verb.

In Ukrainian, perfective verbs normally do not have a true present meaning. Their so-called present-type endings actually give a future meaning.

So:

• заповните = you will fill out / will complete

This is very common in Ukrainian. Perfective verbs often use a simple future like this.

The difference is mainly aspect:

• заповните = perfective
  Focuses on the action as completed: you will fill it out, you will get it done.

• будете заповнювати = imperfective future
  Focuses more on the process: you will be filling it out / will be engaged in filling it out.

So if the idea is that the document will end up completed, заповните is the natural choice.

No. Here it is a statement about the future, not an order.

A command would be:

• Заповніть документ! = Fill out the document!

That is a different form: заповніть, not заповните.

This is a very common thing for learners to confuse, because the forms look similar.

It actually functions as the direct object, so it is in the accusative case.

But for many masculine inanimate singular nouns in Ukrainian, the accusative looks exactly the same as the nominative.

So:

• nominative: документ
• accusative: документ

That is why you do not see any visible change here.

Yes, very often you can.

Ukrainian often leaves out subject pronouns because the verb ending already shows the person and number. The ending -те tells you this is you plural/formal you.

So both are possible:

• Ви заповните документ.
• Заповните документ.

Including Ви can make the subject clearer, more contrastive, or slightly more explicit.

No. Ви заповните документ is the most neutral word order here, but Ukrainian word order is more flexible than English.

Possible alternatives include:

• Документ ви заповните.
• Ви документ заповните.

These alternatives can shift the emphasis:

• Документ ви заповните may emphasize the document
• Ви документ заповните may emphasize you

So the original order is the most neutral, but not the only possible one.

Because Ukrainian has no articles.

So документ can mean:

• a document
• the document

The exact meaning depends on context, not on a separate article word.

That is why a sentence like Ви заповните документ can sound perfectly natural without any equivalent of the or a.