If the customer just opened it in Wordpad and saved it, that would just mean the linebreaks are Windows (CR+LF) as I understand it. In that situation you can use any decent text editor that understands/converts between different linebreaks.
But then I guess you wouldn't be posting if it was that simple. Can you give more details on what the customer did? Are you sure the customer didn't delete the linebreaks?
The best way to understand what you have in your translated file is to use a hex editor to inspect it, and see what lies around the areas where there should be linebreaks. If there's nothing in the file to separate different lines then I think you're pretty much stuffed.