I have created one WPF application and i converted that application into exe. Now i want to run the application while windows startup.Is there any way to startup my app without writing any new code in my WPF?
You will have to do that as part of your installation script, not as part of your application (consider asking the user for consent).
See here for an example: Set that a program has to run at startup from an installer
So technically, the answer to your question is: yes, you can do that without any code changes to your application.