It's a per-filetype registry edit. Here's the example for .doc. If you're
using Office 2007, you would also want to edit .docx.
Open the registry editor & navigate to:
[HKEY_LOCAL_MACHINE\SOFTWARE\Classes\SystemFileAssociations\.doc]
In the right-hand pane, you'll want to edit the value named 'Preview
Details'. The various details are separated by semi-colons. Insert the
string 'System.Document.Wordcount' wherever you want. In this export, it is
the first detail to appear. (This is an edited export, showing only the
PreviewDetails info)
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Classes\SystemFileAssociations\.doc]
"PreviewDetails"="prop:System.Document.WordCount;*System.DateModified;System.Author;System.Keywords;*System.Size;System.Title;System.Comment;System.Category;*System.Document.PageCount;System.ContentStatus;System.ContentType;*System.OfflineAvailability;*System.OfflineStatus;System.Subject;*System.DateCreated;*System.SharedWith"