Can I simultaneously pursue separate masters and PhD degrees? Can I enroll in a masters degree program via correspondence at another university while simultaneously enrolled as PhD as a regular student from University of Delhi?
The answer to the question as stated is almost certainly "yes". A correspondence degree can be pursued by anyone, regardless of occupation, and your occupation as a PhD student shouldn't affect that. Note that your department may discourage this practice, as you would effectively be holding two full-time jobs (or one full-time and one part-time, depending on how quickly you pursue the correspondence degree).