Hello student study certificate by college is enough there's no need submit all previous study certificates. Documents have to be produced for verification are as mentioned below -

1)KCET applications Form

2)Proof of application fee payment

3)Admit card

4)Score card of class 10th standard

5)Score card of 12th standard

6)Two recent passport size Photographs

7)Study certificate counter signed by concerned BEO /DDPI

For more details refer to the link mentioned below - https://www.google.com/amp/s/engineering.careers360.com/articles/kcet-counselling/amp

Feel free to comment if you've any doubt

Good luck