If you are interacting with the Umbraco document API or referencing other Umbraco functionality in your user controls, you must reference the appropriate Umbraco DLLs so that your code will compile and Visual Studio IntelliSense will work.
To include references to these core Umbraco libraries, simply follow these steps:
You can include others, as well; for example, the UmbracoExamine DLL if you are working with Examine for searching, and so on. However, the preceding list is enough to work with the document API and other core Umbraco functions, if you have a need for that.
For examples on how to work with the document API, see Chapter 12