How to add 404 Page not Found custom error in web config in asp.net

Add below code to  web.config:


    <customErrors defaultRedirect="~/PageError.aspx"
                 mode="On">
      <error statusCode="500"
             redirect="~/PageError.aspx"/>
      <error statusCode="404"
           redirect="~/PageNotFound.aspx"/>
    </customErrors>
If you found HTTP 404.0-File not Found

then add you have to add more code given below:

<system.webServer>
    <httpErrors errorMode="Custom" >
      <remove statusCode="404" subStatusCode="-1"/>
      <error statusCode="404" path="~/PageNotFound.aspx" responseMode="Redirect"  />
    </httpErrors>
  </system.webServer>