Introduction:
NCERT textbooks serve as the foundation for the Class 12 Commerce syllabus. However, to gain a comprehensive understanding of the subjects and to enhance knowledge, it is recommended to refer to supplementary and reference books. These books provide additional explanations, examples, practice questions, and alternative perspectives, making the learning process more effective. Here are some recommended supplementary and reference books for Class 12 Commerce.

1. Accountancy:
- TS Grewal's Double Entry Bookkeeping: This book provides a detailed explanation of the fundamental concepts of accountancy. It includes various illustrations, practice problems, and solutions.
- DK Goel's Accountancy: It covers the entire syllabus in a comprehensive manner. The book includes numerous examples, exercises, and solved problems for better understanding.

2. Economics:
- Indian Economic Development by VK Ohri: This book covers all the topics of Indian Economy, including the latest data and case studies. It provides a deeper insight into the subject with the help of illustrations and examples.
- Introductory Microeconomics and Macroeconomics by Sandeep Garg: These books are highly recommended for a clear understanding of micro and macroeconomics. They provide detailed explanations, practical examples, and numerous practice questions.

3. Business Studies:
- Business Studies by Poonam Gandhi: This book covers all the topics of business studies in a comprehensive manner. It includes case studies, practical examples, and practice questions.
- Business Studies by CB Gupta: It provides a detailed explanation of various concepts related to business studies. The book includes case studies, practice questions, and solutions.

4. Mathematics:
- RD Sharma's Mathematics: This book is highly recommended for practicing and mastering mathematical concepts. It includes a wide range of questions categorized according to difficulty levels.
- NCERT Exemplar Problems: This book provides additional practice problems with detailed solutions. It covers all the topics of the NCERT textbook.

Conclusion:
Supplementary and reference books play a crucial role in enhancing the understanding and knowledge of Class 12 Commerce subjects. They provide additional explanations, examples, and practice questions for a comprehensive learning experience. Some recommended books for Class 12 Commerce include TS Grewal's Double Entry Bookkeeping, DK Goel's Accountancy, Indian Economic Development by VK Ohri, Introductory Microeconomics and Macroeconomics by Sandeep Garg, Business Studies by Poonam Gandhi, Business Studies by CB Gupta, RD Sharma's Mathematics, and NCERT Exemplar Problems. These books can greatly assist students in achieving a deeper understanding of the subjects and scoring well in the examinations.