Shows how to get the text from the active document via DTE

GetEditorText.cs

private DTE _dte;

private NAME(Package package)
{
 // ...
 _dte = (DTE) ServiceProvider.GetService(typeof(DTE));
 // ...
}

private static string GetDocumentText(Document document)
{
 var textDocument = (TextDocument) document.Object("TextDocument");
 EditPoint editPoint = textDocument.StartPoint.CreateEditPoint();
 var content = editPoint.GetText(textDocument.EndPoint);
 return content;
}