Tento pas patří Petrovi.

Because the verb patřit (to belong) takes the dative case in Czech.

• Petr = basic dictionary form, called the nominative
• Petrovi = dative form, meaning to Petr

So:

• Tento pas patří Petrovi. = This passport belongs to Petr.

This is one of the important things to learn with Czech verbs: many of them require a specific case, not a preposition like English does.

Yes, when patřit means to belong to someone/something, it normally takes the dative.

Examples:

• Ta kniha patří Marii. = That book belongs to Marie.
• To auto patří mému bratrovi. = That car belongs to my brother.

So when you learn patřit, it is useful to remember it as:

• patřit komu/čemu = to belong to someone/something

That komu/čemu is the Czech prompt for the dative case.

Tento means this.

Czech has a few ways to say this/that, and tento is a common, clear written form for this.

In this sentence:

• tento pas = this passport

You may also hear tenhle pas in spoken Czech, which also means this passport, but sounds more conversational.

A rough comparison:

• tento = more neutral or slightly more formal
• tenhle = more colloquial in speech

Because pas is the subject of the sentence, so it stays in the nominative case.

The sentence structure is:

• Tento pas = the thing being talked about, the subject
• patří Petrovi = belongs to Petr

Since pas is masculine inanimate singular, the nominative form is simply pas.

Also, tento has to match pas in gender, number, and case:

• tento = masculine singular nominative
• pas = masculine singular nominative

So they agree with each other.

Pas is the subject.

Even though English speakers may feel that Petr is somehow the more important person in the meaning, grammatically the sentence is built around the passport:

• This passport = subject
• belongs to Petr = predicate + indirect object in the dative

So Czech treats pas as the thing doing the grammatical action of belonging.

The ending -ovi is a very common dative singular ending for masculine animate nouns, especially personal names.

For example:

• Petr → Petrovi
• Jan → Janovi
• bratr → bratrovi

With male names, you will often see this pattern.

There is sometimes more than one possible dative form for masculine names, but Petrovi is the standard and very common form here.

For the name Petr, the normal form here is Petrovi.

You should not use Petru if you mean the man Petr.
Petru is usually the dative/accusative of the female name Petra, not the male name Petr.

So:

• Petrovi = to Petr
• Petru = usually Petra in another case

That is an important distinction.

The infinitive is patřit.

Patří is the 3rd person singular present tense form, used with he/she/it or with singular nouns.

So:

• patřit = to belong
• pas patří = the passport belongs

Some related forms:

• patřím = I belong
• patříš = you belong
• patří = he/she/it belongs

In this sentence, pas is singular, so patří is the correct form.

Because Czech usually expresses that relationship through the case ending, not with a separate word.

In English:

• to Petr

In Czech:

• Petrovi

The ending -ovi already shows the meaning to Petr, so no extra word is needed.

This is one of the biggest differences between English and Czech grammar: Czech often uses endings where English uses prepositions.

Yes, Czech word order is more flexible than English word order because the case endings show the grammatical relationships.

The most neutral version is:

• Tento pas patří Petrovi.

But you could also hear:

• Petrovi patří tento pas.

That version puts more emphasis on Petrovi, something like This passport belongs to Petr / It is Petr’s passport.

Even though word order can change, the endings still tell you who is who:

• pas stays the subject
• Petrovi stays in the dative

A very natural spoken version would often be:

• Tenhle pas patří Petrovi.

Here:

• tenhle = colloquial this

Both sentences are correct:

• Tento pas patří Petrovi. = perfectly correct, slightly more neutral/written
• Tenhle pas patří Petrovi. = very natural in speech

Yes. Czech often also uses possession with být (to be) plus a possessive form:

• Ten pas je Petrův. = That passport is Petr’s.

This is slightly different in structure, but the meaning is very close.

Compare:

• Tento pas patří Petrovi. = This passport belongs to Petr.
• Tento pas je Petrův. = This passport is Petr’s.

Both are natural, but they use different grammar.

A simple approximate pronunciation is:

• PEH-troh-vee

A few points:

• Stress in Czech is almost always on the first syllable: PE-trovi
• r is rolled or tapped
• the final i is pronounced like ee in see

So the whole sentence is approximately:

• TEN-toh pas PA-tree PEH-troh-vee

That is only an approximation for English speakers, but it is a useful starting point.