Dokumentet vil blive sendt til min chef i morgen.

Because dokumentet is the definite form of dokument.

• et dokument = a document
• dokumentet = the document

In Danish, the definite article is usually added to the end of the noun as a suffix:

• en bil → bilen
• et hus → huset
• et dokument → dokumentet

So Dokumentet means The document.

This is a future passive construction.

• vil = will
• blive = be / become
• sendt = sent

Together, vil blive sendt means will be sent.

So the structure is:

• vil
  • blive
    • past participle

Examples:

• Brevet vil blive skrevet = The letter will be written
• Maden vil blive serveret = The food will be served

Sendt is the past participle of the verb sende (to send).

Main forms:

• at sende = to send
• sender = send / sends / am sending / are sending
• sendte = sent
• sendt = sent (past participle)

In passive constructions with blive, Danish uses the past participle:

• bliver sendt = is being sent / is sent
• vil blive sendt = will be sent

The passive is used when the focus is on the document, not on the person sending it.

Active:

• Jeg vil sende dokumentet til min chef i morgen = I will send the document to my boss tomorrow

Passive:

• Dokumentet vil blive sendt til min chef i morgen = The document will be sent to my boss tomorrow

In the passive sentence, the sender is either unknown, unimportant, or simply not mentioned.

Yes. Danish often has two kinds of passive:

1. blive-passive

   • Dokumentet vil blive sendt ...

2. s-passive

   • Dokumentet vil sendes ...

Both can mean The document will be sent ...

Very roughly:

• blive-passive often sounds a bit more like an event or process
• s-passive is often shorter and common in formal or written Danish

In many contexts, both are possible.

Because the sentence does not say who sends it. Danish, like English, can leave the agent unstated in a passive sentence.

If you want to say who does the sending, Danish usually uses af:

• Dokumentet vil blive sendt af sekretæren i morgen
  = The document will be sent by the secretary tomorrow

So in your sentence, the sender is simply omitted.

Til here means to, showing the recipient or destination.

• sende noget til nogen = send something to someone

So:

• til min chef = to my boss

This is the normal preposition with sende when you mention the person receiving something.

After a possessive like min, din, hans, vores, the noun is normally in the indefinite form, not the suffixed definite form.

So:

• min chef = my boss
• not min chefen

Compare:

• chefen = the boss
• min chef = my boss

This is very common in Danish:

• min bil = my car
• vores hus = our house
• hans dokument = his document

In Danish, chef means boss, manager, or head of something.

Examples:

• min chef = my boss
• afdelingschef = department manager/head

This is a useful false friend for English speakers, because English chef usually means a professional cook. In Danish, the word for a chef in the cooking sense is typically kok.

This is because Danish follows the V2 rule in main clauses: the finite verb usually comes in the second position.

Here:

1. Dokumentet
2. vil
3. blive sendt til min chef i morgen

So even though English speakers may think of will as part of a larger verb phrase, Danish grammar still treats vil as the finite verb that must come second in a main clause.

You can see this more clearly if another element comes first:

• I morgen vil dokumentet blive sendt til min chef.

Now I morgen is first, and vil is still second.

Yes. That is very natural Danish.

• Dokumentet bliver sendt til min chef i morgen
• Dokumentet vil blive sendt til min chef i morgen

Both can refer to the future.

Danish often uses the present tense with a future time expression like i morgen. So bliver sendt can mean is being sent or will be sent, depending on context.

Adding vil makes the future meaning more explicit.

I morgen is a time expression, and Danish allows some flexibility.

Your sentence:

• Dokumentet vil blive sendt til min chef i morgen.

Also possible:

• I morgen vil dokumentet blive sendt til min chef.
• Dokumentet vil i morgen blive sendt til min chef.

The most natural choice depends on what you want to emphasize:

• i morgen at the end: neutral
• I morgen at the beginning: emphasizes tomorrow

A rough pronunciation guide is:

Dokumentet vil blive sendt til min chef i morgen
≈ doh-koo-MEN-ted vil BLEE-we sent til min shef ee MORN

A few notes:

• dokumentet: the final -et is often reduced in normal speech
• blive often sounds closer to blee-we or even more reduced
• chef is pronounced like shef
• i morgen is often pronounced more like ee morn than a fully careful ee mor-gen

If you want to sound natural, listening to native audio is especially helpful with this sentence, because spoken Danish tends to reduce unstressed syllables a lot.