The Diploma in Applied Permaculture Design can be reached by completing the following steps.
1) Introductory course
Usually a 2 day introduction offered all over the world. It can be given by Permaculture Designers with a Diploma and also by people who hold a PDC. This is usually included with any PDC course.
2) PDC: The Permaculture Design Certificate
The next step you take is the PDC. This course comes along in different forms and lengths. However, it has to include given topics. (Ask the Permaculture Association, infamously advertised as "72h by Mollison" course). This course can only be taught by diploma holders.
3. After obtaining your PDC, you are allowed to start using the term Permaculture in business practices, engage in internships and advanced training in Permaculture schools around the globe, begin designing and implementing what you have learned and creating your portfolio. Ask your national Permaculture Organisation for details. In some places you may have to study in your neighboring country depending on the knowledge of your country's teachers.
The education takes a minimum of 2 years but has no time limit; the outcome is the "Diploma of Applied Permaculture Design" . Every student must design 10 projects and be able to present them. This is the same all over the world and holders of this Diploma have undergone these same steps.
-> However, every project is different, every school has different regulations, and a different variety of week-end courses to take during these 2 years. Additionally, every person is different and chooses a different focus.
It is possible to do a self study for this period of time, but your project portfolio will be reviewed by other diploma holders, and networking is important. Doing a physical internship after your PDC will greatly enhance your credibility.