I know that dot net dlls and exe contain their assemblies with them so every body can extract code from it. So please tell me how can i create my own .net obfuscator and if
We must have to use obfuscator and if we are releasing commercial product then it more required. It protects us from unauthorized decompilation and reverse engineering of software. You can use various free as well paid obfuscators. Also for full proof protection you need to use copy protection to prevent unauthorised destrubution.
You can check free obfuscator. This is which I am using to protect my applications.
FxProtect - Free .Net Obfuscator