Project and portfolio management do require some of the same general skills, but despite their similar-sounding names, project management and portfolio management are actually quite different.
Project management, as you know, is the application of knowledge, skills, tools, and techniques to project activities in order to meet project requirements and its importance cannot be over-emphasized.
The operative word in Project Portfolio Management on the other hand, is portfolio. PPM is not primarily concerned with running projects, rather its focus is on choosing which projects to be involved in and how to fund them, based on whether or not they support the goals and objectives of the company. Projects that do not fall within the scope of the company’s objectives are removed from contention.
If you were managing a technology company’s portfolio for example, you would most likely reject a proposed building project, because it doesn’t align with the company’s stated strategy of focusing only on some predefined type of tech projects.