Custom error pages can be implemented in IIS 7 (Windows 2008) and newer by placing a web.config override file in the document root of your web site. Below is example content for custom 403 and 404 status pages:
<?xml version="1.0" encoding="UTF-8"?>
<configuration>
<system.webServer>
<httpErrors>
<remove statusCode="404" subStatusCode="-1" />
<error statusCode="404" prefixLanguageFilePath="" path="/custom404.htm" responseMode="ExecuteURL" />
<remove statusCode="403" subStatusCode="-1" />
<error statusCode="403" prefixLanguageFilePath="" path="/custom403.htm" responseMode="ExecuteURL" />
</httpErrors>
</system.webServer>
</configuration>