What this paper has to prove
A certificate of incumbency answers one question: who may act for the company right now. Italy answers it with a current paper from the business register, which names the officers in post and shows the firm is still live. So how to apostille a Certificate of Incumbency comes down to ordering that paper and taking it to the right desk.
The stamp is an apostille: a single certificate that proves the signature and seal on your paper are real. It says nothing about whether the named director is any good at the job. To apostille a Certificate of Incumbency in Bari, then, all the desk needs is a paper whose signature it can trace.
Which desk stamps it
A register paper is issued by a public body, so it counts as administrative and the Prefettura (Prefecture) handles it. You therefore apostille a Certificate of Incumbency in Italy at the Prefettura for the province where that office sits. Deeds and acts signed by a notary follow the other track, to the Procura della Repubblica, and mixing the two costs a day.
Cost and waiting time
The apostille cost for a Certificate of Incumbency in Bari is a public charge, not a service price: €16 per document as a tax stamp, and some papers are exempt. The register office charges its own small fee for the paper itself. How long the stamp takes is set by the queue that week, so do not promise a bank a firm date.
Banks, boards and tenders
This is the paper a foreign bank wants before it lets an Italian company open an account. Tender boards ask for it to check that the person signing the bid really may. Buyers ask for it at closing, and a foreign notary may ask for it before a deed. In each case it travels beside the founding deed rather than replacing it.
Requests sometimes arrive worded as the legalisation of a Certificate of Incumbency in Bari, which is the older name for the same errand. Italy has been a Hague Convention country since 1978, so one stamp is enough for other member states. Whether the country your file is going to belongs to that group is worth confirming in writing.
Language and dates
Two things trip companies up at the last moment. The first is language: a reader who works in one language will want a sworn translation of the paper and often of the stamp too. The second is timing, because a paper that was current when you queued may look stale by the time it lands on a lawyer's desk abroad.