Pasted

var application = new Application();
object missing = Type.Missing;
object filename = "c:\\data\\sample.docx";
object False = false;
application.DisplayAlerts = WdAlertLevel.wdAlertsNone;
 
Document document = application.Documents.Open(
    ref filename, ref missing, ref missing, ref missing,
    ref missing, ref missing, ref missing, ref missing, ref missing,
    ref missing, ref missing, ref False, ref missing, ref missing,
    ref missing, ref missing);
Hyperlinks links = document.Hyperlinks;
 
for (int i = 1; i <= links.Count; i++)
{
    object index = i;
    Hyperlink link = links.get_Item(ref index);
    link.Address = "http://www.google.com";
}
 
if(document != null)
{
    try
    {
        document.Save();
    }
    catch {}
    document.Close(ref missing, ref missing, ref missing);
}
 
if (application != null) application.Quit(ref missing, ref missing, ref missing);
 
GC.Collect();
GC.WaitForPendingFinalizers();
GC.Collect();
GC.WaitForPendingFinalizers();