Help please I am unable to reinstall my HP 5540 inkjet printer

Please reset the printing system and then install the printer. Instructions for each are in the links below.

Reset Printing System feature

Adding a printer

If you are running Catalina, please see this:

Long-serving forum member Kurt Lang posted this on Saturday Oct 24:

From sources familiar with the matter, HP Inc asked Apple to revoke its printer driver code-signing certificates. It appears this request backfired as it left users unable to print. A HP Inc spokesperson told us on Friday night (Oct 23):

“We unintentionally revoked credentials on some older versions of Mac drivers. This caused a temporary disruption for those customers and we are working with Apple to restore the drivers. In the meantime, we recommend users experiencing this problem to uninstall the HP driver and use the native AirPrint driver to print to their printer.”

HP supplied a new driver on Friday to fix the issue:

ftp://ftp.hp.com/pub/softlib/software12/HP_Quick_Start/osx/Installations/Essentials/hp-printer-essentials-S-5_14_8_4.pkg

However, that "fix" is producing this error for some users:

"Matterhorn.framework" will damage your computer…

If you're seeing that, try this fix. Go to System Preferences, select Printers and Scanners. Select your printer from the list then delete (-) it. Then add (+) your printer back and select the generic driver to use.