Moramo ovjeriti ovu potpisanu izjavu.

Moramo means we must or we have to.

It is the 1st person plural present-tense form of morati (to have to / must):

• moram = I must
• moraš = you must
• mora = he/she/it must
• moramo = we must
• morate = you all / you formal must
• moraju = they must

In Croatian, you usually do not need to say mi (we), because moramo already shows who is doing the action.

After morati, Croatian normally uses an infinitive.

So the pattern is:

• moramo + infinitive = we have to + verb

Here:

• moramo ovjeriti = we have to certify / notarize

This is very similar to English have to do something.

Examples:

• Moram ići. = I have to go.
• Moramo potpisati dokument. = We have to sign the document.
• Moramo ovjeriti ovu izjavu. = We have to certify this statement.

Ovjeriti means something like:

• to certify
• to authenticate
• to notarize
• sometimes to validate officially

The exact English translation depends on context. In document-related situations, it often means that a document gets some kind of official confirmation, for example from a notary, office, or authority.

So this sentence is not just about signing a statement. It means the signed statement still needs official verification/certification.

They refer to two different actions:

• potpisanu comes from potpisati = to sign
• ovjeriti = to certify / notarize / officially validate

So:

• potpisana izjava = a signed statement
• ovjeriti izjavu = to certify/notarize the statement

This implies a sequence like:

1. someone signs the statement
2. then it gets officially certified

That is why both ideas appear in the same sentence.

Because this whole phrase is the direct object of ovjeriti, so it is in the accusative case.

The base form is:

• ova potpisana izjava = this signed statement
  (nominative)

But after the verb, as the object, it becomes:

• ovu potpisanu izjavu = this signed statement
  (accusative)

Since izjava is a feminine singular noun, the accusative singular endings are:

• ova → ovu
• potpisana → potpisanu
• izjava → izjavu

So all three words change to match feminine singular accusative.

Because they all agree with the noun izjavu.

Croatian adjectives and words like this/that change to match the noun in:

• gender
• number
• case

Here the noun is:

• izjava = feminine
• singular
• accusative

So the related words must match it:

• ovu = this
• potpisanu = signed
• izjavu = statement

That matching is called agreement.

Potpisanu is a form of potpisan, which means signed.

It behaves like an adjective, even though it comes from the verb potpisati (to sign). In this sentence it describes izjavu:

• potpisana izjava = signed statement

So you can think of it as a verbal adjective / participial adjective meaning signed.

Its form here is feminine singular accusative to agree with izjavu:

• nominative: potpisana izjava
• accusative: potpisanu izjavu

Yes. Ovu is the accusative feminine singular form of ova (this).

So:

• ova izjava = this statement
• ovu izjavu = this statement (as object)

English does not show that case change, but Croatian does.

You can also think of ovu as this particular or this one, depending on context.

No, it is not stated explicitly.

Croatian often leaves out subject pronouns when the verb form already makes the subject clear. Since moramo already means we must, there is no need to add mi.

So:

• Moramo ovjeriti ovu potpisanu izjavu. = normal
• Mi moramo ovjeriti ovu potpisanu izjavu. = possible, but more emphatic

Adding mi would usually stress we in contrast to someone else.

Yes, Croatian word order is more flexible than English, because case endings show grammatical roles.

The neutral order here is:

• Moramo ovjeriti ovu potpisanu izjavu.

But other orders are possible for emphasis, for example:

• Ovu potpisanu izjavu moramo ovjeriti.
  = It is this signed statement that we have to certify.

• Moramo ovu potpisanu izjavu ovjeriti.
  = also possible, with slightly different rhythm/emphasis

Even when word order changes, the endings still show that ovu potpisanu izjavu is the object.

All of these can be possible depending on context.

Izjava often means:

• statement
• declaration
• written statement
• sometimes form or declaration document in administrative contexts

In official or legal language, declaration may sound more natural in some cases. In general language, statement is often the safest choice.

So ovu potpisanu izjavu could be:

• this signed statement
• this signed declaration

The exact best translation depends on the situation.

Ovjeriti is perfective.

That means it refers to the action as a completed whole: getting the document officially certified.

Its imperfective partner is usually ovjeravati.

Here, perfective makes sense because the sentence is about a specific task that needs to be completed:

• Moramo ovjeriti ovu potpisanu izjavu.
  = We have to get this signed statement certified.

If you used the imperfective, it would sound more like an ongoing/repeated process, which is not the normal idea here.

Sometimes yes, but not always.

Ovjeriti does not automatically mean notarize in every context. It more generally means officially certify/authenticate.

Depending on the document and the country-specific procedure, it could involve:

• a notary
• a court
• an office
• another authorized authority

So if the real-life context is notarization, notarize is a good translation. If the context is broader, certify or authenticate may be safer.