Are dogs allowed?
Dogs are allowed on much, but not all of the PCT. Generally, they need to be on leash. The regulations affecting you and your dog vary depending on the agency that manages the stretch of the trail. There are no PCT-specific dog regulations. There are different rules for different places (national parks, wilderness areas, state parks, etc) and you’ll cross many jurisdictional boundaries.
Working service dogs assisting visitors with disabilities are often allowed where other dogs are not. Know the regulations. There is no central or generally accepted certifying body for service animals/dogs. Americans with Disabilities Act (ADA) is generally followed by the federal agencies, and is a good guide to what is and what is not a service animal. See: http://www.ada.gov/service_animals_2010.htm Be aware that it is quite likely that you will be contacted by a ranger to inquire as to the legitimacy of your dog as a service animal.