Some countries require legalisation of documents. In many cases, a legalization of sales invoices is only needed by the Chamber of Commerce. In some cases legalization by Embassy is required.
The Chamber of Commerce (CoC) verifies the name and signature on the document and legalizes this signature. After authentication, you the document will be returned to you, with the required legalization stamp of the Chamber of Commerce on it.
For certain countries legalization is required by the Embassy and/or the Ministry of Foreign Affairs.
Different embassies charge different costs and how long the legalization takes depends on the country (between 1 until 10 working days).