The Overwrite property returns or specifies whether an existing file with the specified name is overwritten. The default value of this property is True. If a file with the given name already exists and this property is set to False, the export operation fails.
Examples:
The following VBA example fails while exporting the active document if the file img.gif already exists in the folder C:\Temp.
Sub Test()
Dim opt As New StructExportOptions
Dim flt As ExportFilter
opt.Overwrite = False
Set flt = ActiveDocument.ExportEx("C:\Temp\img.gif", cdrGIF, cdrCurrentPage, opt)
flt.Finish
End Sub