Custom invoice won't show

In Display...Views I changed the orders/invoice.php file for both beez5 (myfront end template) and bluestork (my backend template), but the changes don't show when I am in the order screen back end and click on the invoice button.

Also, my shipping invoice pops up in a lightbox, the email button brings up a lightbox, but the invoice button no longer shows a lightbox, but downloads the invoice instead (which is the wrong looking invoice). Not sure if that is related. Seems there is something wrong with my Invoice button.

That's because you have the attach invoice plugin installed and published.
In that case, the invoice button gives you the PDF of the invoice instead of the popup. And if you want to edit the invoice generated by the plugin, you need to copy the file plugins/hikashop/attachinvoice/attachinvoice/invoice.php to media/plugins/invoice.php and edit that file.

I cannot find the attach invoice plugin to install it. Will this allow for my invoice to be sent with the email notification?

Kind regards,

Yes. It will be attached to the order status notification sent when the order is confirmed.

You can find it here:
www.hikashop.com/en/component/hikashop/product/cid-18.html