Sažetak je gotov, pa ću ga poslati e‑mailom.

to be

Breakdown of Sažetak je gotov, pa ću ga poslati e‑mailom.

• htjeti: will (future auxiliary)
• pa: so
• e-mail: email

Questions & Answers about Sažetak je gotov, pa ću ga poslati e‑mailom.

Why is it Sažetak je gotov and not Sažetak je gotova/gotovo?

Because sažetak (summary/abstract) is a masculine noun in Croatian. The short adjective gotov (finished/ready) must agree with it in gender and number:

• masculine singular: gotov
• feminine singular: gotova
• neuter singular: gotovo
• plural: gotovi/gotove/gotova (depending on gender)

So with sažetak → Sažetak je gotov.

What does je do here? Could it be omitted?

Je is the present tense of biti (to be), 3rd person singular: he/she/it is. In this kind of sentence (X je gotov = X is finished), je is normally required.
You might see Sažetak gotov. only in very informal, note-like styles (headlines, messages), but the full, standard sentence uses je.

Why is there a comma before pa?