Jeg må genåbne dokumentet, fordi jeg glemte at tilføje datoen.

Here må means something like have to / need to / must.

In this sentence, Jeg må genåbne dokumentet means the speaker has to reopen the document because of a mistake.

A useful thing to know is that må can have slightly different shades of meaning depending on context:

• must / have to → obligation or necessity
• may → permission, in some contexts

Here it clearly means must / have to, not permission.

Also, må is a modal verb, so in the present tense it does not take at before the next verb:

• Jeg må genåbne not
• Jeg må at genåbne

Genåbne means reopen, while åbne means open.

The prefix gen- often means again / re- in Danish. So:

• åbne = open
• genåbne = reopen

This is similar to English prefixes like re-:

• write → rewrite
• open → reopen

So the sentence uses genåbne because the document was already opened before and now needs to be opened again.

Because dokumentet is the definite form and means the document.

In Danish, the definite article is often attached to the end of the noun instead of being a separate word like English the.

For a neuter noun like et dokument:

• et dokument = a document
• dokumentet = the document

So -et here is the definite ending for a neuter singular noun.

For the same basic reason: datoen means the date.

But dato is a common gender noun, not a neuter noun. So its definite singular ending is -en:

• en dato = a date
• datoen = the date

Compare:

• et dokument → dokumentet
• en dato → datoen

So Danish uses different definite endings depending on the noun’s gender.

Because glemte is the past tense form of the verb glemme.

Here the speaker is describing a completed action in the past:

• jeg glemte = I forgot

The form glemt is the past participle, not the simple past. You would use glemt with another verb, for example:

• Jeg har glemt datoen = I have forgotten the date

So:

• glemte = forgot
• har glemt = have forgotten

In this sentence, the simple past glemte is the correct form.

Because at tilføje is the infinitive, meaning to add.

After glemte, Danish often uses an infinitive construction:

• glemte at tilføje = forgot to add

This works much like English:

• I forgot to add the date

So here:

• glemte = forgot
• at tilføje = to add

A helpful comparison:

• Jeg prøver at læse = I am trying to read
• Jeg glemte at skrive = I forgot to write

Tilføje means to add.

It is made from:

• til = to, toward, onto
• føje = an older verb element related to adding/joining

In modern Danish, it is best learned as one full verb: tilføje.

Examples:

• tilføje en dato = add a date
• tilføje et navn = add a name
• tilføje information = add information

So glemte at tilføje datoen means forgot to add the date.

Good question. In this sentence, fordi jeg glemte at tilføje datoen has normal subject-verb order:

• jeg glemte

That is completely standard and correct.

Danish subordinate clauses often show their special word order most clearly when there is an adverb like ikke, aldrig, or ofte. For example:

• fordi jeg ikke glemte det not
• fordi ikke jeg glemte det

So the subordinate-clause pattern matters, but in your sentence there is no adverb to make the difference visible. That is why it simply looks like:

• fordi jeg glemte ...

Because fordi introduces a subordinate clause: because I forgot to add the date.

In standard Danish writing, it is normal to put a comma before a subordinate clause introduced by words like:

• fordi = because
• hvis = if
• at = that
• da = when/since

So:

• Jeg må genåbne dokumentet, fordi jeg glemte at tilføje datoen.

This comma helps show the structure of the sentence.

Yes, but the meaning changes a bit.

• Jeg må genåbne dokumentet = I have to / need to reopen the document
• Jeg skal genåbne dokumentet = I will / am supposed to / have to reopen the document

Very roughly:

• må often sounds like necessity because of the situation
• skal often sounds more like a plan, instruction, or obligation

In your sentence, må fits well because the speaker realizes that reopening is necessary as a result of forgetting the date.

No, not in normal Danish.

You need the subject in the subordinate clause:

• fordi jeg glemte at tilføje datoen

Unlike in some informal English patterns, Danish does not usually omit the subject here. Each clause needs its own subject unless the structure is different.

So this is correct:

• Jeg må genåbne dokumentet, fordi jeg glemte at tilføje datoen.

Not:

• Jeg må genåbne dokumentet, fordi glemte at tilføje datoen.

The å in må is a rounded vowel, somewhat like the vowel in British English law or more, though the exact sound depends on accent.

So må is approximately like moh with a rounded vowel.

A few pronunciation notes:

• å is a separate letter in Danish
• it often sounds like a broad o/aw sound
• må is usually pronounced as one long syllable

Also note that genåbne contains å too:

• gen-åb-ne

For English speakers, the hardest part is often making the rounded vowel clearly enough.

Yes.

Danish can use glemme in at least two common ways:

1. glemme + noun

   • Jeg glemte datoen = I forgot the date

2. glemme at + infinitive

   • Jeg glemte at tilføje datoen = I forgot to add the date

The difference is similar to English:

• I forgot the date = the thing itself slipped your mind
• I forgot to add the date = you failed to do the action

In your sentence, the speaker is not saying the date itself was forgotten in memory, but that the action of adding it was forgotten.

Yes. Both are possible.

• genåbne dokumentet = reopen the document
• åbne dokumentet igen = open the document again

The first is more compact and often feels a bit more formal or precise. The second is very natural too.

So these are both acceptable:

• Jeg må genåbne dokumentet
• Jeg må åbne dokumentet igen

The meaning is nearly the same.