Hi @ember541 :
The file that you received from the conversion should be able to be opened in 2018. I would go to zoom.us and do a screen share session with your client. Share the file you received from support (and not the one you opened in 2019). Then open that on his computer in 2018. It should open.
Let me know if that worked. You could also download a trial of 2018 and open it on your computer and then send the client a backup of that. You can get a free trial here.
Lynda
