This is labeled as a self-help book, but I wouldn't recommend it being used by someone on their own. If you're trying to come to terms with whether you have PTSD, are in the throws of suffering from it or trying to deal with it, this book's exercises will trigger you in a variety of ways. The exercises are geared to have you remember trauma, relive it, confront coping mechanism symptoms, make yourself aware of negative behaviors, all of which is more than likely to enhance trauma, trigger further negative experiences, and escalate issues if done without a support framework.
I would recommend using this book in tandem with a therapist or other professional who is versed in trauma processing and supporting those with PTSD. This not only provides the safe space most sufferers struggle to create for themselves and which is absolutely necessary for this type of work, but helps retrain and heal the Limbic system to expect positive results from going through difficult and triggering situations.