How to programmatically edit all hyperlinks in a Word document?

Dim doc As Document
Dim link, i
'Loop through all open documents.
For Each doc In Application.Documents
    'Loop through all hyperlinks.
    For i = 1 To doc.Hyperlinks.Count
        'If the hyperlink matches.
        If LCase(doc.Hyperlinks(i).Address) = "http://www.yahoo.com/" Then
            'Change the links address.
            doc.Hyperlinks(i).Address = "http://www.google.com/"
            'Change the links display text if desired.
            doc.Hyperlinks(i).TextToDisplay = "Changed to Google"
        End If
    Next
Next

Here is a link to all the Hyperlink Methods and Properties