When you type a file name in the Open, Save, or Save As dialog box, Word may automatically try to complete the file name for you. This tweak can be used to enable or disable this behaviour.

To enable or disable this behavior, follow the next steps:

1. To open the Registry Editor click on the Start button on your taskbar, then click on Run and type "regedit" and click on OK to start the utility.
   
   
2. Expand HKEY_CURRENT_USER\Software\Microsoft\Office\[version]\Common\General (see picture 1).
   
   

   Picture 1

3. Create a new String value, or modify the existing value, called "Use AutoComplete" and set it according to the value data above.
    
4. The modifications you made will be in effect after you reboot your PC.