The section 3 and section 4 of the Patent Act, 1970 gives list of inventions which are not patentable:

1. Inventions that are frivolous or obviously contrary to well-established natural laws.

2. Inventions whose primary use or commercial exploitation could be contrary to public order, morality, or cause serious prejudice to human, animal, plant life, health, or the environment.

3. Mere discovery of scientific principles, abstract theories, or any living or non-living substance occurring in nature.

4. Mere discovery of a new form of a known substance without enhanced efficacy, or a new property, use, or process, unless it results in a new product or employs at least one new reactant.

5. Substance obtained by mere admixture resulting only in the aggregation of the properties of the components or a process for producing such substance.

6. Mere arrangement, re-arrangement, or duplication of known devices functioning independently in a known way.

7. Methods of agriculture or horticulture.

8. Processes for medicinal, surgical, curative, prophylactic, diagnostic, therapeutic, or other treatment of humans or animals.

9. Plants, animals, seeds, varieties, species, and biological processes for their production or propagation (except microorganisms).

10. Mathematical or business methods, computer programs per se, or algorithms.

11. Literary, dramatic, musical, artistic works, or aesthetic creations, including cinematographic works and television productions.

12. Mere schemes, rules, or methods of performing mental acts or playing games.

13. Presentation of information.

14. Topography of integrated circuits.

15. Inventions that are traditional knowledge 

16. Inventions relating to atomic energy.

1. Filing: File an international application with a Receiving Office (RO) or directly with the International Bureau (IB) of WIPO. Comply with PCT formality requirements and pay the necessary fees. In India, PCT applications are filed at appropriate patent offices based on territorial limits.

2. International Search: An International Searching Authority (ISA) identifies relevant prior art and provides a written opinion on the invention's potential patentability. The Indian Patent Office, Delhi Branch, acts as an ISA upon receipt of the prescribed fee.

3. International Publication: 18 months after the earliest filing date (Priority Date), the content of the international application is disclosed worldwide.

4. International Preliminary Examination (optional): Upon request, an ISA conducts an additional patentability analysis, usually on an amended version of the application. The Indian Patent Office, Delhi Branch, acts as an International Preliminary Examination Authority (IPEA) upon receipt of the prescribed fee.

5. National Phase: After 30/31 months from the earliest filing date of the initial application, the applicant pursues the grant of patents directly before the national or regional patent offices of the desired countries. In India, the maximum time limit to enter the national phase is 31 months. To enter the national phase, an application corresponding to the international application is made using Form 1.

1. Decide on the PCT national phase filing in India: After receiving the international search report and the written opinion, decide the PCT national phase filing in India

2. Meet national requirements: Each country may have specific requirements for entering the national phase, such as paying national fees and filing translations of the application. These requirements must be fulfilled before the end of the 30th or 31st month from the priority date for most PCT Contracting States' patent offices.

3. Appoint best Patent Lawyers in India or best Patent Attorneys in India or best Patent Agents in India

4. Consult the PCT Applicant's Guide: For more general information on national phase entry, refer to the PCT Applicant's Guide, National Phase. Specific information concerning fees and national requirements can be found in the national chapters for each PCT Contracting State in the same Guide.

5. Submit required documents and pay fees: File the necessary documents and pay the required fees to the national patent offices of the selected countries within the specified time limit to complete the national phase entry process.