I understand that you have an HP ENVY 7645 e-All-in-One Printer that will not copy. It actually scans and prints properly but copying results in a blank page being ejected from the printer. I would like to help with that.
It is odd that you are able to scan the same document successfully, but when you do a copy a blank page comes out of the printer. Scanning and copying use the same parts in the printer. If one works the other should work as well.
I would start by performing a power reset on the printer.