I signed a confidentiality agreement with a startup, but they haven’t offered me a job yet. I don’t have a copy of the signed document, and they’re refusing to give it to me. I have a recording of them saying they won’t share the document and that it stops me from working in e-commerce. I want to send them a notice demanding a copy of the agreement and ensuring it’s invalid without the job offer.

You can send a notice demanding a copy of the confidentiality agreement. While the agreement may be valid, Indian law generally requires consideration for a contract to be enforceable, and the lack of a job offer could be argued as a lack of consideration.
The recording of them refusing to share the agreement and restricting your work in e-commerce could be helpful evidence in any legal action.
You should consult with a lawyer to discuss your specific situation and best course of action.