Kan du sende dokumentet senest fredag, så jeg kan læse det i weekenden?

Because this is a question used as a request.

In Danish, yes/no questions usually have the verb before the subject:

• Kan du sende dokumentet? = Can you send the document?
• Du kan sende dokumentet. = You can send the document.

So kan du ... is the normal question pattern. In this sentence, that question functions as a polite request, just like English Can you send ...?

Not necessarily. Here kan du is mostly a polite way of asking someone to do something.

It can literally mean are you able to, but in everyday use it often works like English:

• Can you send it by Friday?

So in this sentence, it sounds like a normal, polite request rather than a question about physical ability.

Because dokumentet is the definite form: the document.

Danish usually adds the definite article to the end of the noun:

• et dokument = a document
• dokumentet = the document

So instead of using a separate word like English the, Danish often attaches it as a suffix.

Senest fredag means by Friday at the latest.

• senest = at the latest / no later than
• fredag = Friday

So the idea is that Friday is the deadline.

Examples:

• senest i morgen = by tomorrow at the latest
• senest kl. 10 = no later than 10 o’clock

Because in Danish, days of the week often appear without a preposition in time expressions, especially with deadlines or scheduling.

So:

• senest fredag = by Friday at the latest
• vi ses mandag = see you Monday

You can also hear på fredag, especially for this coming Friday, but senest fredag is a very natural fixed expression for a deadline.

Here så means so or so that.

It connects the two parts of the sentence:

• Kan du sende dokumentet senest fredag
• så jeg kan læse det i weekenden?

So the second part gives the purpose/result:

• ... so that I can read it at the weekend / over the weekend

After så in this kind of sentence, Danish normally uses ordinary clause order:

• jeg kan læse det

not inversion:

• kan jeg læse det

So even though English learners may expect the verb to move forward, it does not do that here.

A useful pattern to remember is:

• Gør X, så jeg/vi/han kan ...
  = Do X, so that I/we/he can ...

Example:

• Kom tidligt, så vi kan starte med det samme.
  = Come early, so we can start right away.

Because Danish, like English, often uses a pronoun after a noun has already been mentioned.

So:

• dokumentet = the document
• det = it

Instead of saying læse dokumentet, Danish naturally says læse det if the reference is already clear.

Because dokument is a neuter noun in Danish:

• et dokument

Neuter nouns normally take the pronoun det.

Compare:

• en bog → den
• et dokument → det

So:

• dokumentet ... det is correct.

I weekenden means during the weekend / over the weekend.

The preposition i is commonly used with periods of time in Danish. In this expression, Danish uses the definite form:

• weekenden = the weekend

So the whole phrase is an idiomatic time expression:

• i weekenden = at the weekend / over the weekend

Because i weekenden is the normal idiomatic expression when you mean during the weekend.

• i weekenden = over the weekend
• i en weekend = during one weekend / on a certain weekend

So the definite form does not sound unusual to Danish speakers here; it is simply the standard way to express this idea.

It is neutral and polite.

Kan du ...? is a very common and acceptable way to ask someone to do something in Danish, especially in work or everyday situations.

The sentence does not sound overly formal, but it is perfectly polite. If needed, you could make it a bit softer with words like:

• Kan du måske sende dokumentet ...? = Could you perhaps send the document ...?
• Vil du sende dokumentet ...? = Would you send the document ...?

But the original sentence already sounds natural and courteous.