Hi MishMirand,
Thank you for becoming a member of the HP Support community. I understand that you are getting full color page ad printing out randomly form your Photosmart C4780 printer.
This printer predates HP’s ePrint feature and the answer that Dragon-Fur gave you about using HP Connected is correct. To better assist you, would you please provide some further information:
1) How is the printer connected (USB cable or wireless)?
2) In your other post, you indicated that the printer stopped working then started again and that is when the ads began printing. If you remember, what steps did you take to get the printer working?
3) Are you able to scan one of the ads and add it to your next post? That would greatly assist in trying to determine what is printing and where it is coming from.
Thank you.