Hello,
In order to fill forms for Calcutta University, you shoumd go to their official website where you will find the link for "admission open". You then have to click on the form for your particular course and fill it up along with the required documents. They will ask for your digital signature which you will have attach by writing it on a paper and clicking a picture of it, same goes with your passport size photo.
I hope this helps,
All the best
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