bill.sue :
I'm selling my HP printer 5610 and the guy who wants to buy it is running Windows 7. Will this printer work on Windows 7?
Absolutely.
There is a specific Win 7 driver for it:
https://support.hp.com/us-en/drivers/selfservice/hp-officejet-5600-all-in-one-printer-series/441142/model/441143