The book "Principles of Quantum Mechanics" by Paul Dirac, first published in 1930, is a renowned work in the field of quantum mechanics. While I cannot provide direct links to copyrighted material, there are several resources where you may be able to find the book in PDF format legally and for free. Here are a few options to explore:
Online Libraries: Check online libraries such as Project Gutenberg (www.gutenberg.org) or Archive.org (www.archive.org). These platforms offer a wide range of books, including older works that have entered the public domain.
Academic Institutions: Some academic institutions and universities provide free access to digital libraries and archives. Explore the websites of renowned universities with strong physics programs to see if they offer open access to their collection of scientific literature.
Open Access Journals and Repositories: Look for open-access journals and repositories that focus on physics and quantum mechanics. Websites like arXiv (arxiv.org) host a vast collection of scientific papers, including many classic works in the field. While "Principles of Quantum Mechanics" might not be available directly, related papers and resources can be found.
Online Forums and Communities: Engage with online physics communities, forums, or discussion platforms. There might be individuals or groups who have shared links to resources or can guide you to specific websites where you can find the book you're seeking.
Remember to respect copyright laws and ensure that the version you find is legally available for free distribution. Some works may still be protected by copyright, and obtaining them through unauthorized means would be a violation of intellectual property rights.