Moram provjeriti važenje osobne iskaznice prije nego što predam zahtjev.

Yes. Morati (moram, moraš, mora…) is a modal verb and it’s normally followed by the infinitive:

• Moram provjeriti = I have to check
• Moraš doći = You have to come

In everyday Croatian, you can also hear a da-clause in some contexts, but with morati the infinitive is the standard, most natural choice.

It’s aspect:

• provjeriti (perfective) = to check (once), to verify / complete the check
• provjeravati (imperfective) = to be checking, to check repeatedly/regularly

In your sentence, Moram provjeriti… implies a single, completed check before doing something else.

važenje means validity (literally “being valid”). It’s a verbal noun formed from važiti (to be valid). Croatian often uses this noun in administrative language:

• provjeriti važenje osobne iskaznice = check the validity of the ID card

You’ll also commonly see rok važenja = expiry/validity period.

Because važenje takes a complement in the genitive to mean “validity of something.” So osobne iskaznice is genitive singular: of the ID card.

By contrast, provjeriti osobnu iskaznicu would mean to check the ID card itself (e.g., examine it), while provjeriti važenje osobne iskaznice focuses specifically on whether it’s still valid.

It’s genitive singular (feminine). You can recognize it because:

• the noun iskaznica (nom. sg.) becomes iskaznice (gen. sg.)
• the adjective osobna becomes osobne (gen. sg. fem.)

Together: (važenje) osobne iskaznice = the validity of the personal ID card.

prije nego što means before (that) and introduces a subordinate clause. In many situations, speakers shorten it to prije nego (especially in speech), but prije nego što is very common and perfectly standard.

Both are usually translated as before.

In Croatian, after time conjunctions like prije nego što / kad / čim, you often use the present tense even when you’re talking about a future event—English would use before I submit, not before I will submit. Also, the verb predam is perfective present, which naturally points to a completed future action:

• predam (from predati, perfective) ≈ I (will) submit/hand in (and it will be done)

So prije nego što predam zahtjev = before I submit the application.

• predam = 1st person singular present of predati (perfective): to hand in/submit (once, completed)
• predajem = 1st person singular present of predavati (imperfective): to be handing in / to submit repeatedly

Here you’re talking about one completed submission, so predam is the natural choice.

zahtjev is accusative singular because it’s the direct object of predati (to submit/hand in something):

• predati zahtjev = to submit an application/request

For this masculine inanimate noun, accusative singular looks the same as nominative singular: zahtjev.

Croatian word order is fairly flexible, but neutral/admin style would keep it close to what you have. You can rearrange for emphasis, for example:

• Prije nego što predam zahtjev, moram provjeriti važenje osobne iskaznice. (emphasizes the “before” part)
• Moram prije predaje zahtjeva provjeriti važenje osobne iskaznice. (more formal; before the submission of the application)

The original order is very natural and clear.

A practical approximation for English speakers:

• važenje ≈ VAH-zhe-nyeh (the ž is like the s in measure)
• iskaznice ≈ ees-KAZ-nee-tseh (final ce like tseh)

If you can produce ž (/ʒ/) and keep vowels clear (Croatian vowels are “pure”), you’ll be understood well.