Lični dokument je u torbi.

Because lični is an adjective agreeing with dokument.

• dokument is masculine, singular, and here it is in the nominative case because it is the subject.
• So the adjective must also be masculine singular nominative: lični.

A few matching examples:

• lični dokument
• lična karta
• lično pismo

The adjective changes form depending on the noun it describes.

Dokument is masculine.

That matters because adjectives and some other words must match its gender. That is why you get:

• lični dokument and not lična dokument or lično dokument

Je means is. It is the 3rd person singular present form of biti (to be).

So:

• Lični dokument je u torbi.
• literally: Personal document is in bag.

In normal English we must say is, and in Serbian you also need je here.

Because after u meaning in, when you are talking about a location, Serbian uses the locative case.

• base form: torba = bag
• locative singular: torbi

So:

• u torbi = in the bag

This is a very common pattern with feminine nouns ending in -a:

• škola → u školi
• soba → u sobi
• torba → u torbi

No. U can take different cases depending on meaning.

• u + locative = location, in/inside
• u + accusative = motion, into

Compare:

• Lični dokument je u torbi. = The document is in the bag.
• Stavljam lični dokument u torbu. = I am putting the document into the bag.

So u torbi shows location, while u torbu would show movement toward the inside of the bag.

Because Serbian does not have articles like English a and the.

So Lični dokument je u torbi can mean:

• The ID document is in the bag
• A personal document is in the bag

Which one sounds best depends on context. Serbian usually leaves that information to the situation, word order, or extra words if needed.

It can mean identity document / personal document, but in everyday speech people very often say more specific things, such as:

• lična karta = ID card
• pasoš = passport
• vozačka dozvola = driver’s license

So lični dokument is understandable and correct, but it may sound a bit broader than English ID.

Yes. Serbian word order is more flexible than English.

This sentence can also appear as:

• U torbi je lični dokument.

That version puts more focus on where the document is.

However, keep in mind that je is a clitic, so it usually appears in the second position in the sentence or clause. That is why you get:

• Lični dokument je u torbi.
• U torbi je lični dokument.

Both are natural, but the emphasis changes.

Because je is a clitic in Serbian. Clitics usually go in the second position.

In:

• Lični dokument je u torbi

the first unit is Lični dokument, and je comes right after it.

In:

• U torbi je lični dokument

the first unit is U torbi, and again je comes right after that unit.

This is a very important Serbian word-order pattern.

A simple English-friendly approximation is:

• lični ≈ LEECH-nee, but with č pronounced like ch in church
• torbi ≈ TOR-bee

A few sound notes:

• č = a hard ch sound
• lj in lični is not there here, so do not pronounce it like ly
• Serbian pronunciation is generally quite phonetic, so words are usually pronounced close to how they are spelled

It is in the nominative case because it is the subject of the sentence.

You can tell because the sentence is saying something about the document:

• Lični dokument = the thing being talked about
• je u torbi = what is being said about it

So the basic structure is:

• subject: Lični dokument
• verb: je
• place phrase: u torbi

Normally, no. In a full standard sentence like this, je should stay.

• correct: Lični dokument je u torbi.
• not standard as a full sentence: Lični dokument u torbi.

You might hear shortened speech in very informal situations, but for learners it is best to keep je here.