Sir,
If the process undertaken by the job worker does not amount to manufacture under Section 2 (f) of Central Excise Act, 1944, then he may simply return the inputs after processing without payment of duty under the cover of the challan originally received. If the process undertaken by the job worker amounts manufacture then he will pay duty and issue an excisable invoice. The duty paid by the job worker is available as credit to the principal manufacturer.
After introduction of Finance Act, 1994 if the process undertaken by the job worker does not amount to manufacture he is considered to provide a service and the same is chargeable to service tax. In this case also he will issue an invoice under Service Tax Rules, 1994 and the principal manufacturer is eligible to take credit of the service tax paid by the job worker. However, Sl. No. 30 (c) of Notification No. 25/2012-ST dated 20.6.2012 as amended (with effect from 1.7.2012) stipulated that any goods excluding alcoholic liquors for human consumption on which appropriate duty is payable by the principal manufacturer is exempted from payment of service tax. That is if the principal manufacture uses the job worked goods in the manufacture of final product and pay duty on the same then the job worker is exempted from payment of service tax.