Could not load file or assembly ''Microsoft.SharePoint.Client.Runtime', Version=15.0.0.0

Dear All

This is the code which I used. And I have added Microsoft.SharePoint.dll .

using Microsoft.SharePoint.Client;

internal static HttpClientHandler GetClientHandler(string spSiteUrl, string username, string pwd)
{
//Creating Credentials
var passWord = new SecureString();
foreach (var c in pwd) passWord.AppendChar(c);
var credential = new SharePointOnlineCredentials(username, passWord);

HttpClientHandler handler = new HttpClientHandler() { Credentials = credential };

//Getting authentication cookies
Uri uri = new Uri(spSiteUrl);
handler.CookieContainer.SetCookies(uri, credential.GetAuthenticationCookie(uri));

return handler;
}

The Error shows like this :

Could not load file or assembly 'Microsoft.SharePoint.Client.Runtime, Version=15.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c' or one of its dependencies. The system cannot find the file specified.WorkflowActivity: System.IO.FileNotFoundException: Could not load file or assembly 'Microsoft.SharePoint.Client.Runtime, Version=15.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c' or one of its dependencies. The system cannot find the file specified

Added following dll in this project.

.dll :- Microsoft.SharePoint.Client.Runtime
Runtime version :- v4.0.30319
version :-15.0.0.0

.dll :- Microsoft.SharePoint.Client
Runtime version :- v4.0.30319
version :- 15.0.0.0

Thanks