public static string CreateNewFileName(string fullName, string oldString, string newString)
{
string oldName = fullName;
StringBuilder strBuilderNewName = new StringBuilder(fullName);
int index = fullName.LastIndexOf(oldString);
if (index != -1)
{
strBuilderNewName.Replace(oldString, newString, index, oldString.Length);
oldName = strBuilderNewName.ToString();
}
return oldName;
}