registration

not mandatory if engaged exclusively in the supply of exempted goods

A supplier shall not be liable for registration if his aggregate turnover consists of only such goods and/or service which are not liable to tax or wholly exempt from tax under this act.

But, persons making any inter-State taxable supply shall be required to be registered under this Act irrespective of the threshold.

For a transaction to qualify as a taxable supply, the supply should be leviable to GST – i.e., it should not be covered within the meaning of ‘non-taxable supply’ as defined under Section 2(78) – i.e., alcoholic liquor for human consumption. This implies that supplies enjoying a full exemption from tax by way of an exemption notification would also be treated as taxable supplies.

Here, printed books are exempted vide N.N. 02/2017 but will be treated as taxable supply, as said above. Hence, you should apply for registration.

URD is can't make inter State supply. So, You want registration if you sell your goods to inter state.