Proofs of origin (documents)
Even if your product is originating (i.e. fulfill the Basic rules and its provisions), you need still to verify the product was sent from the “originating” country and arrive to the EU without being manipulated in another country, apart from the mere operations needed for keeping the product in good conditions.
You need to verify the specific conditions on this issue and documents needed to demonstrate the fulfilment of this rule contained in the relevant set of rules of origin.
See also: your product is wholly obtained or sufficiently transformed by considering the elements specified in "wholly obtained/sufficiently transformed goods" section, "minimal operations" section, "cumulation" section and "tolerance or de minimis" section