PS4 Add-on to a disc

Do you mean DLC (downloadable content)? Yes so, yes, it's totally possible.
Thanks for replying. I have Horizon Zero Dawn on a CD. I the purchased The Frozen Wilds add-on. However, after downloading it refuses to install. When clicked if says game files not found.
I do I resolve this?
This can happen if your disc is from one geographic region and your PSN online account is from a different country. If there is a mismatch, Sony won't let you install the DLC.
Strange.. If its from the same developer, what difference does the origin of country matter?