Sir,
Rule 9 of Cenvat Credit Rules, 2004 stipulates that-
9. (1) The CENVAT credit shall be taken by the manufacturer or the provider of output service or input service distributor, as the case may be, on the basis of any of the following documents, namely :-
(a) an invoice issued by-
(i) a manufacturer or a service provider for clearance of -
(I) inputs or capital goods from his factory or depot or from the premises of the consignment agent of the said manufacturer or from any other premises from where the goods are sold by or on behalf of the said manufacturer;
(II) inputs or capital goods as such;
(ii) an importer;
(iii) an importer from his depot or from the premises of the consignment agent of the said importer if the said depot or the premises, as the case may be, is registered in terms of the provisions of Central Excise Rules, 2002;
(iv) a first stage dealer or a second stage dealer, as the case may be, in terms of the provisions of Central Excise Rules, 2002;
It does not distinguish the original or duplicate copy of the invoice. Therefore you can take credit even on the basis of original copy of the invoice.