When you begin typing a file or folder name in Common dialog box (Open / Save As) in an application, the Auto Complete drop-down will appear by default. To prevent the AutoComplete dropdown from appearing, follow these steps.
Click Start, Run and type REGEDIT and press Enter
Navigate to the following key:
In the right pane, create a new REG_DWORD value named AutoComplete In File Dialog
Double-click AutoComplete In File Dialog value and set it's value to 0, and then click OK.
Close Registry Editor
Automate the above with these REG files
Turn off autocomplete for file dialog boxes | Undo