Selecting

The Documents collection starts at 1.

Application.Documents.Item(2) 
Application.Documents(2) 
Application.Documents("Temp.doc") 

Dim objDocument As Document 
objDocument = Application.ActiveDocument 
objDocument = ActiveDocument 

The ActiveDocument is read only and cannot be used to set the active document

Documents("Temp.doc").Activate 

WholeStory Method

The WholeStroy method expands a Range or Selection object to include the entire story
The following two lines are equivalent.

objRange.WholeStory 
objRange.Expand Unit:=wdUnits.wdStory 

Content Property

The content property returns a Range object that represents the main document.
The following two lines are equivalent

ActiveDocument.Content.Select 
ActiveDocument.StoryRanges(wdStoryType.wdMainTextStory).Select