Symptoms
How can one add the HtmlAgilityPack from Nuget to a K2 Project to be referenced in custom code?
Diagnoses
When adding this Nuget package to a C# application, it looks to be just referencing the 'HtmlAgilityPack.dll' assembly.
Resolution
Assembly references can be added to a K2 Project as a "Process Reference andgt .NET", as per:
http://help.k2.com/onlinehelp/k2blackpearl/userguide/current/webframe.html#pr01.html