Here are some MSDN documentation links (assume Word ≥2013 unless noted) to the various objects and methods and enumerations mentioned in ++poj's post:

• Object Model = start here for documentation on the objects in the Word OLE
• Selection Object = all the methods and properties for $Word->Selection
• Selection.EndKey Method = shows that you need to pass EndKey a Unit => WdUnits value
• WdUnits Enumeration = the values of each of the enumerations in WdUnits
• Enumerations = "Table of Contents" for all the ≥2013 Enumeration Types
• Enumerated Constants = Word2003 Version, with all the enums on one page (quick reference, but possibly out of date)