Hello, category certificate in prescribed format is required for the students applying for the reservation category. But you can produce the undertaking form in the meanwhile if the certificate cannot be produced within the application deadline. You can download the undertaking letter from this link https://josaa.nic.in/webinfocms/Public/View.aspx?page=73

But it is necessary that you also apply for the certificate meantime since you will be needed to submit later when required.

Hope this helps.