Unable to scan HP8740 All-in-One ...

If you do not want to go the AirPrint route click on this link,

https://support.hp.com/gb-en/drivers/selfservice/hp-officejet-pro-8740-all-in-one-printer-series/7902055

Click the + button next to the Driver Product Installation Software and download the HP Smart app.

When downloaded run the app, this will guide you through setting up your printer and download any necessary

software or drivers. Once you have done that Reset the Printing System.

Reset the Mac printing system to solve a problem - Apple Support

If your HP OfficeJet Pro 8740 All-in-One is an Apple AirPrint-enabled device, then remove that device from Printers & Scanners, and add it again as an AirPrint device. You must specifically choose AirPrint. You can then delete the offending HP files as they appear. They are not necessary, and with an invalid security certificate they are not doing anything anyway.

You do not require any non-Apple software to scan documents: Scan images or documents using your Mac - Apple Support.

Refer to Connect an AirPrint printer to a Wi-Fi network. Sometimes it's necessary to reboot your router to recognize a newly added AirPrint device, so it couldn't hurt to do that: unplug its power cord, let it rest a moment, plug it back in.

Hello John,

Those error messages occur when trying to scan any documents from within the Preview app ... not from any HP app. I can print from my iMac or copy directly from the printer. The messages are displayed when the Preview app tries to connect to the printer ... and that is since the latest OS update.

My printer is ethernet connected. Why would I connect it as an AirPrint enabled device ?

My printer is ethernet connected.

Ethernet or wireless does not matter to AirPrint.

Why would I connect it as an AirPrint enabled device ?

So that you can remove the offending HP files and use Preview as you intend.