Dear aspirant,

As per the information provided by University of Delhi, you need a Central OBC certificate at the time of admission. Digitally signed documents are valid during the time of admission provided that they are attested by the concerned SDM.
For more information, I request that you visit the link provided below:

Microsoft Word - FAQs related to admission against Reserved Category.docx (du.ac.in) (https://www.du.ac.in/du/uploads/COVID-19/01072020_FAQs%20related%20to%20admission%20against%20Reserved%20Category.pdf)
If you still have doubts, I request that you further clarify your query.

Hope this helps!