Jeg vil vedhæfte dokumentet til min email, før jeg sender den.

Vil is the present tense of ville. In a sentence like this, it often shows intention or a planned future action.

So Jeg vil vedhæfte ... suggests something like I want to / I’m going to attach ....

A learner often compares it with skal:

• vil = intention, willingness, plan
• skal = obligation, requirement, something you are supposed to do

So this sentence sounds more like a personal intention than a duty.

Because vil is a modal verb.

After Danish modal verbs such as:

• vil
• kan
• skal
• må
• bør

the next verb is normally in the bare infinitive, without at.

So:

• Jeg vil vedhæfte dokumentet = correct
• Jeg vil at vedhæfte dokumentet = incorrect

Compare with a verb that does require at:

• Jeg prøver at vedhæfte dokumentet

Vedhæfte is the infinitive form of the verb, the form you would find in a dictionary.

Some common forms are:

• at vedhæfte = to attach
• vedhæfter = attaches / am attaching
• vedhæftede = attached
• vedhæftet = attached

In this sentence, it appears after vil, so it stays in the infinitive:

• vil vedhæfte

Because Danish usually puts the definite article at the end of the noun.

• et dokument = a document
• dokumentet = the document

So dokumentet is the definite form.

Also, dokument is a neuter noun, which is why the indefinite form uses et:

• et dokument
• dokumentet

Because email / e-mail / mail is normally treated as a common-gender noun in Danish:

• en email / en e-mail / en mail

For singular possessives:

• common gender → min
• neuter gender → mit

So:

• min email = correct
• mit email = incorrect for this noun

Compare:

• min mail
• mit brev (brev is neuter: et brev)

Because Danish commonly uses the pattern:

• vedhæfte noget til noget
  = attach something to something

So in this sentence:

• dokumentet = the thing being attached
• til min email = what it is being attached to

This works quite similarly to English attach the document to my email.

Because før jeg sender den is a subordinate clause.

In Danish, many writers put a comma before a subordinate clause. However, Danish has had more than one accepted comma system, so you may also see the sentence written without that comma.

So both of these may occur:

• Jeg vil vedhæfte dokumentet til min email, før jeg sender den.
• Jeg vil vedhæfte dokumentet til min email før jeg sender den.

The version with the comma is completely normal.

Because Danish often uses the present tense after time words and conjunctions such as:

• før = before
• når = when
• efter = after
• inden = before

So før jeg sender den is the normal way to say before I send it, even though the sending has not happened yet.

This is very similar to English, which also says:

• before I send it

not usually:

• before I will send it

Because før introduces a subordinate clause, and subordinate clauses in Danish do not use normal main-clause V2 word order.

In a main clause, Danish often puts the finite verb in second position:

• Nu sender jeg den.

But in a subordinate clause, the order is typically:

• conjunction + subject + finite verb + object

So:

• før jeg sender den = correct
• før sender jeg den = incorrect here

Den refers to email, not dokumentet.

This is important because Danish pronouns must match the gender of the noun they replace:

• en email → den
• et dokument → det

So:

• før jeg sender den = before I send the email
• før jeg sender det = before I send the document

Even though dokumentet is closer in English thinking, the thing you normally send here is the email, so den is the natural pronoun.

There are other natural options.

Many Danish speakers also use:

• e-mail
• mail

So you may also hear or see:

• Jeg vil vedhæfte dokumentet til min e-mail ...
• Jeg vil vedhæfte dokumentet til min mail ...

All of these are understandable and natural. The exact spelling and choice often depends on personal or stylistic preference.