To install Official .NET driver for MongoDB, run the following command in the Package Manager Console.
PM> Install-Package mongocsharpdriver -Version 1.10.0
check for the latest version here
Call using statements at minimum:
using MongoDB.Bson;
using MongoDB.Driver;
Sometimes there will also need additional:
using MongoDB.Driver.Builders;
using MongoDB.Driver.GridFS;
using MongoDB.Driver.Linq;