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Your customer may haven't installed a PDF reader, -igotexas-us.
It can be the reason why they're unable to view the details of the estimate as well as the logo.
If they've installed, let's make sure that that it's updated to the latest version. You can share this link with them on how to update the Adobe Reader: Update Adobe Reader.
When you're ready to convert the estimate to an invoice, you can check this guide: Convert an estimate into an invoice in QuickBooks Online.
Feel free to get back to me if there's anything that I can help. Keep safe!