As a newbie to writing, I can't comment on how to dramatically portray the lifelong impact of childhood trauma. But as a person with PTSD, I can confirm that as Stu W explained "flashbacks, obsession, avoidance, and a high-adrenaline state" are real symptoms. Others include general depression and anxiety. But an important feature is triggers. A trigger can be a smell, an object, a sound etc. Anything that reminds the person of the event. As the name implies, a trigger is a stimulus that leads to a strong response of anxiety or flashback. It can cause a fight-flight-freeze response.
As an example, I know a soldier who can't sleep near a window for fear of snipers. And a woman who is afraid of turbans because she was assaulted by a man wearing one.
The person may also be plaited by destructive thoughts or beliefs about themselves. Things like I deserved what happened, my life is cursed, etc.
In the book I'm writing, I am planning a critical scene where the character freezes with a flash back at a very critical moment. More subtle features can be woven in as things like lack of trust, avoidance of people, addictions, risk taking, avoidance of triggering situations, etc.
Another common attribute is the effect and damage it has on relationships. Also the burden it puts on people around the character who can see the traits and the self destructiveness that the character can't see in himself.
I would avoid reading the DSM. It is too technical and dry. There are many biographies of people with PTSD. Many news articles. You should be able to do some surface reading to get an idea of the experience. This type of reading will give you a better feel of how it affects people than anything written from a psychological, sterile point of view.