W biurze muszę skanować dokumenty.

Because after w meaning in for a fixed location, Polish uses the locative case.

• dictionary form: biuro = office
• locative singular: biurze

So:

• w biurze = in the office

If you said w biuro, it would be ungrammatical in standard Polish for this meaning.

Biurze is the locative singular form of biuro.

This is a very common pattern in Polish:

• w domu = in the house
• w sklepie = in the shop
• w biurze = in the office

The locative is used after certain prepositions, especially when talking about location, such as w, na, o, przy.

Muszę is the 1st person singular form of musieć, which means must / have to.

So:

• muszę = I must / I have to

Other forms of musieć include:

• musisz = you must
• musi = he/she/it must
• musimy = we must

In this sentence, the subject is understood from the verb, so Polish does not need a separate ja.

Because Polish usually drops subject pronouns when the verb already makes the subject clear.

• muszę already means I must
• so ja is not necessary

You could say Ja muszę skanować dokumenty, but that would usually add emphasis, something like:

• I have to scan the documents
• Me, I have to scan the documents

The neutral version is simply Muszę skanować dokumenty.

After musieć, Polish uses the infinitive of the second verb.

So the structure is:

• muszę + infinitive
• I have to + verb

Examples:

• Muszę pracować. = I have to work.
• Muszę czytać. = I have to read.
• Muszę skanować dokumenty. = I have to scan documents.

This is similar to English have to scan, where scan stays in its base form.

Dokumenty is the accusative plural form, because it is the direct object of skanować.

You are scanning what? → dokumenty

For this noun, document = dokument, the plural looks like this:

• nominative plural: dokumenty
• accusative plural: dokumenty

Because dokument is an inanimate masculine noun, its accusative plural is the same as its nominative plural.

Polish has no articles, so there is no direct equivalent of a / an / the.

That means:

• w biurze can mean in an office or in the office
• dokumenty can mean documents or the documents

The exact meaning depends on context.

This is one of the big differences from English.

Yes. Polish word order is more flexible than English because the endings show grammatical relationships.

The neutral order here is:

• W biurze muszę skanować dokumenty.

But you could also hear:

• Muszę skanować dokumenty w biurze.
• Dokumenty muszę skanować w biurze.

These versions can sound more natural in different contexts depending on what is being emphasized.

Very roughly:

• W biurze muszę skanować dokumenty. → emphasis on in the office
• Muszę skanować dokumenty w biurze. → more neutral in many situations
• Dokumenty muszę skanować w biurze. → emphasis on documents

They express different ideas:

• w biurze = in the office → location
• do biura = to the office → movement toward a place

Compare:

• Jestem w biurze. = I am in the office.
• Idę do biura. = I am going to the office.

So in your sentence, w biurze is correct because the sentence describes where the scanning happens, not movement.

Skanować is the imperfective verb. In Polish, aspect matters a lot.

• skanować = to scan, in a general / repeated / ongoing sense
• zeskanować = to scan completely, to finish scanning

So:

• Muszę skanować dokumenty. can suggest a task or ongoing duty: I have to scan documents
• Muszę zeskanować dokumenty. would suggest completing them: I have to scan the documents / get the documents scanned

If the sentence is about a regular work responsibility, skanować is very natural.

A rough English-friendly pronunciation is:

• muszę ≈ MOO-sheh

A bit more accurately:

• mu- sounds like moo
• sz sounds like English sh
• ę at the end is often pronounced roughly like eh or a nasalized vowel, and in everyday speech it may sound close to e

So muszę is commonly heard close to MOO-she / MOO-sheh.

A rough guide is:

• biurze ≈ BYOO-zheh

More detail:

• biu sounds somewhat like byoo
• rz here sounds like zh, like the s in measure
• final e is like eh

So you can think of it as BYOO-zheh.

The standard Polish verb is skanować, with sk, not sc.

It is a normal Polish verb, borrowed and adapted to Polish spelling and grammar.

You can conjugate it like other Polish verbs:

• skanuję = I scan
• skanujesz = you scan
• skanować = to scan

So even though it comes from international vocabulary, it behaves like a regular Polish verb.