Refer below links.

https://social.msdn.microsoft.com/Forums/windows/en-US/354f193a-1841-487a-bd65-40e396e385bf/code-for-generating-license-key-in-c?forum=winforms

https://www.codeproject.com/Articles/11012/License-Key-Generation

sir i want to prevent piracy. Right now i am generating license key and emailed to office. facing issue if firewall is installed on system. So want to change this process. Insted of email the license key can we generate a patch or something bat file genrated on users system. user will email this file to office and after that we can send him same or diffrent file license key. after that users can start using the software.

For creating patch file refer below link.

Creating MSI / Setup and Patch file for Windows Forms Application

Thanx for your response. I have solve this.