Learn Hardcore Norwegian: Jobbsøknaden må bli sendt inn før fristen. - The job application must be sent in before the deadline.

Norwegian forms compound nouns by joining words together. Here jobb (job) + søknad (application) = jobbsøknad. To make it definite (“the job application”), you add the suffix -en, giving jobbsøknaden.

What does må mean in this sentence? Is it the same as skal?

Må expresses necessity or obligation, equivalent to English must. Skal can mean shall, will, or express a plan or schedule. If you said jobbsøknaden skal sendes inn, it would sound more like a stated plan or requirement set by someone else, but not as strong an obligation as må.

Why do we use bli sendt inn here? Could we say sendes inn instead?

Norwegian has two passive forms:
1) The -s passive, e.g. sendes inn.
2) The bli-passive, e.g. bli sendt inn.
Both are correct:
– Jobbsøknaden må sendes inn før fristen.
– Jobbsøknaden må bli sendt inn før fristen.
The bli-passive often emphasizes the action as a process or is a bit less formal than the -s passive.

Why is før fristen used? Could I use innen fristen instead?

Yes, both are common:
– før fristen literally means before the deadline.
– innen fristen means by/until the deadline, including the very last moment.
Nuance: før stresses something finishes before the point in time; innen allows up to and including that point.

Can I move før fristen to the front? How does word order work here?

Norwegian follows the V2 rule: the finite verb stays in position two. If you front the adverbial, you still keep the verb second:
“Før fristen må jobbsøknaden bli sendt inn.”
Here Før fristen is first, må is second (the verb), and jobbsøknaden is third (the subject).

Who is doing the sending? The sentence doesn’t say.

This is the passive voice, so the agent (who sends it) is omitted. It’s more formal or impersonal. If you want to specify the actor, switch to active:
“Du må sende inn jobbsøknaden før fristen.”
Here du (you) is the subject doing the action.

Why does inn come after sendt instead of before?

The verb sende inn is separable. In infinitive and present tense you split it (sender inn), but in perfect or passive the prefix stays attached to the participle: sendt inn.