I think I am not alone in having problems using my LaserJet pro 400 with MacOS Catalina.
The problems I have been having are:-
(1) Using the HP Scan App I can't scan on the glass.flatbed. I just get the instruction to load the Document Feeder even when I have gone out of my way to select the Flatbed option!
(2) Printing PDF's is hit & miss. Sometimes the printer will print. However, even after I have turned on & off the printer (as suggested) I normally get Error 79 message & no document printed. Also, when I say I manage to get a PDF printed it is only a partial success. I've so far only managed to get the printer to print one page of a range!
I have been using my printer for several years in the Windows environment without any problems. It is not the printer because I have just tested it using a Windows PC & it's not me, because, as I've stated, I know what I'm doing having used the Printer/Scanner for years in the Windows environment for years. I'm beginning to wonder if I have made a mistake going from Windows to Apple Mac.
This seems a classic case where either Hp or Apple have not tested their latest software(s) adequately! Am I being paranoid in suspecting that HP concentrates on Windows because their WIndows App is far superior & easier to use than the Apple MacOS APP.
Incidentally, I have downloaded several times the HP Driver to see if that would resolve the problem. No difference at all.
Please, either Apple or HP get their act together.