YOU MAY GET SEAT ONLY IN IITs THROUGH DS CATEGORY.

Two supernumerary seats are preferentially allocated in every Institute for candidates who qualify under the DS category. A DS candidate must be in the CRL to be eligible for preferential allocation under the DS category. Candidates who are eligible for seat allocation under the DS category will also be considered under their category [viz., GEN, GEN-EWS, OBC-NCL, SC, ST, GEN-PwD, GEN-EWS-PwD, OBC-NCL-PwD, SC-PwD and ST-PwD]. For example, if a candidate belongs to the OBC-NCL category and is also eligible for admission under the DS category, then the candidate will be considered for seat allocation in an academic program of an IIT in the following order: first for OPEN seats, followed by OBC-NCL category seats, and then for seats under DS category.

That means if you are eligible to get a seat under open or other categories, the need of DS certificate does not take place. You can use DS category only if you are not eligible to get a seat in an IIT through open or other categories.