Cops can suffer from PTSD the same as soldiers can, especially those who have undergone firefights and other high pressure scenarios. Being a cop doesn't automatically cause PTSD, though, and it's important to remember that most cops will never see a scenario like the ones we see on TV, with guns blazing and people dying.
Cops have a difficult job that requires professionalism in the face of sometimes horrific circumstances. No amount of training can prepare a person, cop or otherwise, to witness extreme violence and the dangers associated with it. Similar to military soldiers, cops must run into situations that most people would run away from, and doing so in certain circumstances could certainly trigger PTSD.
There are lots of cops that suffer from PTSD. Whether it is from the stresses and traumas that occur on the job, whether it comes from a trauma that happend as part of their daily life or if it is a prexisting condition, there are too many cops that suffer from PTSD on the force.
This is an overgeneralized question. Of course there will be some cops with PTSD depending on what kinds of situations they've encountered while on duty or before they joined the force. Some cops will never go through a traumatizing experience where firearms or violence is involved and some will. It all depends on the person.