I'm glad to have you here in the Community. Let's ensure you'll be able to send invoices to your customers.
To begin with, if you're sending invoices through a web browser to WhatsApp, please ensure that you'veupdated your Adobe Reader/Acrobat. If you've already updated it, and the invoice still has a black background, I suggest performing browser troubleshooting. Issues like this are usually the result of accumulated cache.
We can start by accessing your account through a private browser. You can refer to these shortcut keys to open a private window in all supported browsers: