Hi Chaitanya,
According to your description, my understanding is that you want to enforce mandatory fields no matter when users drag and drop or upload documents in form.
Per my knowledge, when we upload multiple documents(drag documents) to the library in SharePoint 2013, we will not get the prompt for filling the mandatory fields. However, the documents uploaded will not be checked in until the required fields are filled with
data.
To get the goal, we need to create custom solutions to achieve this goal or use Enhanced Document Upload product which is not free in this link:
http://sharepointsnapple.com/enhanced-document-upload/.
Best regards.
Thanks
Victoria Xia
TechNet Community Support
