Excise duty on export sales

Hello Sir/Madam,

I have been auditing a Partnership Firm. The firm purchases leather and manufactures Leather Jackets and exports it. Since it is an export, they do not need to pay excise duty. Their sales are like this. 99% of the entire sale is finished products which are exported and 1% is unfinished leather which are sold in local. 

So,

In this case, what are their implications under Excise Act?

Should they acquire Excise License for sure?

And should they file Nil Excise Return in this case?

Please explain me and it would be helpful if can get Section numbers along with the explanations and where can I find those provisions in the act.

Thank you in advance.