I have a file hosted on the disk along with my website that I want to read .Not sure how do I access the file when I use System.Environment.CurrentDirectory it point to a D
There is an environment variable called HOME in your website's environment that will get you part way there.
You can access it using razor syntax or in code (C#). For example, suppose you have a file called data.txt that is at the root of your site with the default document and the rest of your files. You could get it's full path like this.
@{ var dataFileName = Environment.GetEnvironmentVariable("HOME").ToString() + "\\site\\wwwroot\\data.txt"; }
You can find this out on your own using the Site Control Management/"Kudu". For example, if your website is contoso.azurewebsites.net, then simply navigate to contoso.scm.azurewebsites.net. In here you can learn all about the file system and environment variables available to your website.