Copy paste and cut paste

Question

       
        Hi,
                Now I am working on windows applications,

                I have written some logic to accept required specialcharacters and alphabets and digits in keypress events.Its working while I am trying to enter the data in my text box but my requirement foail for copy paste or cut paste to textbox.
I have tride to solve this problem in keydown event but I unable to get result.
and for example :Ctrl+V
I put break point at this event procedure(keydown) and I press "Ctrl" key then immediatly this event has fired before I press "V" key so can you tel me how to resolve my problem.