I have described how to work with MongoDB in Sitecore in this answer.
Applying it for your case, the code will be similar to this:
MongoDbDriver driver = MongoDbDriver.FromConnectionString("analytics");
MongoDbCollection collection = driver["FormData"];
Guid formId = new Guid("insert-some-guid-here");
MongoCursor<FormData> cursor =
Query<FormData>.EQ(_ => _.FormID, formId));
IList<FormData> results = cursor.ToList();
Note that I'm using a
System.Guid object to define the form ID. You should not use binary IDs in C# code.
The C# driver can automatically map data to strongly-typed models. I assume that the collection you're using in your question contains WFFM data. If that is the case, all you'll need to do is use WFFM's data class
FormData. It's already registered in the driver, so just reference
Sitecore.WFFM.Abstractions.dll in your project and add the following directive in the beginning of your C# file: