Is it possible to develop ptsd by just reading violent books and watching violent media?

Diagnostic Criteria. To actually meet diagnostic criteria for ptsd one has to have actually experienced a traumatic event. So after watching a violent movie while one could experience symptoms similar to posstrauma symptoms like anxiety, nightmares, hypervigilance, etc. One will likely not receive a formal diagnosis of ptsd. Therapy will help anyway even if the symptoms exist without a traumatic event. Feel better!
Not likely. Reading books would would be a quite unlikely source of ptsd. Watching movies might, but probably only if the person was already sensitized to the type of trauma being shown. I had a patient sexually traumatized as a young child who had ptsd after watching silence of the lambs. I doubt strongly she would have had that reaction to reading the book.
Maybe. It's not very likely. But, everyone is different. Some people may be "sensitive" enough to do so.