You write it, someone else certifies it
Unlike a register extract, an invoice comes from your own printer. That is why no desk will stamp it raw: first the chamber of commerce for the province certifies that the signature on it belongs to your firm. Keep the wording plain, sign in ink, and never send a version that differs from the one the buyer holds.
Sellers who ask how to legalize a Commercial Invoice are almost always answering a bank or a customs office abroad. Both want the seller's own figures vouched for by someone outside the firm. So the chain starts inside the chamber, not inside your accounts office.
The state mark on a certified invoice
Once the chamber has signed, the embassy legalization of a Commercial Invoice in Catania picks up at the Prefettura. That office belongs to the state and sits in the province capital, and it confirms the chamber official's signature. Court rulings and notary deeds take the other road, to the Procura della Repubblica at the court.
What the mission charges and how long it holds
Two very different costs meet here. To legalize a Commercial Invoice in Catania you pay a €16 tax stamp, the marca da bollo, on the Italian side. The mission then sets its own fee, and some tie that fee to the value shown on the invoice, so ask what applies before you print. Allow 10–15 business days, or 3–5 business days on the quick lane.
Why buyers insist on the stamped copy
Money moves against paper, not against promises. The consular legalization of a Commercial Invoice in Italy is often a condition in a letter of credit, so the bank holds payment until the stamped sheet lands. Customs at the far end may also want it before duty is worked out and the load released.
Keep the whole trade file telling one story. The invoice, the origin sheet, the packing list and the transport papers should agree on the goods, the amounts and the parties. A clerk abroad who finds two versions of the same line will pick the one that costs you more, or simply stop and ask.
Is the consular step required for that buyer?
Ask before you build it into a quote. Whether the embassy attestation of a Commercial Invoice in Catania is required depends on the buyer's country. Several markets take a single-step certification and nothing beyond it. Put the question to the receiving authority or the buyer's broker in writing, then price the job on their answer rather than on habit.