Hello Ashutosh, 

If you wish to apply for Delhi University, you can surely do so, and make sure to register before June 14th, 2019, which is the last date for Undergraduate Courses' Registration. 

According to the recent law, a student with drop-year can apply for Delhi University;  however 2.5% would be deducted from your best of four, since you are changing your stream from science to Humanities.

No extra document for a Drop Year is needed; hoever, make sure you have a Character certificate issued from last school attended, not less than 6 months old.

I hope this was helpful!