Kad završim, proslijedit ću izvještaj šefici i kolegici iz drugog odjela.

Both kad and kada mean when here. Kad is simply the shorter, very common form in everyday Croatian. Kada can sound a bit more formal or careful, but in this sentence either one is correct:

• Kad završim...
• Kada završim...

The meaning stays the same.

In Croatian, after words like kad meaning when, a future event is often expressed with the present tense of a perfective verb.

So kad završim literally looks like when I finish, but it naturally means when I have finished / when I finish in the future.

This is very normal Croatian usage. English often uses a present form in these clauses too:

• When I finish, I’ll send...

So Croatian and English are actually similar here.

Because after kad in this kind of time clause, Croatian normally does not use the future auxiliary ću. It uses the present form of a perfective verb instead:

• correct: Kad završim...
• not natural here: Kad ću završiti...

So the rule is basically:

• main clause: future can be expressed with ću
• time clause with kad: usually perfective present

Završim comes from završiti, which is a perfective verb. Perfective verbs usually refer to a completed action as a whole.

That is why kad završim means when I finish / once I’m done.

The imperfective partner is usually završavati. Very roughly:

• završiti = to finish, to complete
• završavati = to be finishing, to finish repeatedly/in process

In this sentence, the perfective form is the natural choice because the speaker means a single completed action.

This is how Croatian writes the future tense when the auxiliary ću comes after the infinitive.

With Future I, you can have:

• ću proslijediti
• proslijedit ću

When ću comes after the infinitive, the final -i of the infinitive is dropped in writing:

• proslijediti
  • ću → proslijedit ću

So proslijedit ću is the standard written form.

Because ću is a clitic, and clitics in Croatian usually go in the second position of the clause, not in the very first position.

In the main clause here, the first full word is proslijedit, so ću comes right after it:

• Kad završim, proslijedit ću izvještaj...

You could also rearrange the sentence, for example:

• Kad završim, izvještaj ću proslijediti šefici i kolegici...

That is also grammatical. The placement changes the emphasis a bit.

Croatian usually drops subject pronouns when they are not needed, because the verb ending already shows the person.

Here:

• završim = I finish
• ću with the verb = I will forward

So ja is unnecessary unless you want emphasis or contrast:

• Ja ću proslijediti izvještaj, ne netko drugi.
  = I will forward the report, not someone else.

Izvještaj is the direct object of proslijediti, so it is in the accusative singular.

But izvještaj is a masculine inanimate noun, and for many masculine inanimate nouns, the accusative singular looks the same as the nominative singular.

So:

• nominative: izvještaj
• accusative: izvještaj

That is why the form does not change visibly here.

Because they are the recipients of the report, so they are in the dative singular.

The verb proslijediti often works like to forward something to someone:

• proslijediti izvještaj šefici
• proslijediti izvještaj kolegici

For these feminine nouns, the dative singular is:

• šefica → šefici
• kolegica → kolegici

So the sentence means the report is being forwarded to the boss and to the colleague.

Yes, that is the most natural reading.

Izvještaj is singular, and šefici i kolegici are two coordinated recipients, so the sense is:

• I will forward the report to the boss and to the colleague from the other department.

In other words, one report is being sent or passed on to both of them.

The most natural interpretation is that it describes only kolegici:

• šefici i kolegici iz drugog odjela
• = to the boss and to the colleague from the other department

So the boss is just the boss, while the colleague is the colleague from another department.

Grammatically, Croatian often attaches this kind of phrase to the nearest sensible noun, and here that is kolegici.

Because the preposition iz means from/out of and it requires the genitive case.

So:

• drugi odjel = another/the second department in dictionary-style form
• after iz → iz drugog odjela

Both words change to genitive singular:

• drugi → drugog
• odjel → odjela

That is why you get iz drugog odjela = from the other department.

Proslijediti means to forward, to pass on, or to send along.

In this sentence, it suggests that the speaker is passing the report on to the boss and the colleague, probably after finishing it or after finishing some related task.

It is a very common verb in office and email contexts, for example:

• Proslijedit ću ti poruku. = I’ll forward the message to you.
• Proslijedila je mail šefu. = She forwarded the email to the boss.

Yes. In standard Croatian, when a subordinate clause comes before the main clause, it is normally separated by a comma.

So:

• Kad završim, proslijedit ću izvještaj...

That comma is the standard punctuation, just like English often writes:

• When I finish, I’ll forward the report...

Yes, Croatian word order is fairly flexible, though the emphasis may change.

For example, these are all possible with roughly the same core meaning:

• Kad završim, proslijedit ću izvještaj šefici i kolegici iz drugog odjela.
• Kad završim, izvještaj ću proslijediti šefici i kolegici iz drugog odjela.
• Izvještaj ću, kad završim, proslijediti šefici i kolegici iz drugog odjela.

The original version is natural and neutral. Other orders may put extra focus on izvještaj, on the timing, or on the action of forwarding.