I’ve posted the following resource to the group “Free Textbooks at UC San Diego”:
Introduction to Philosophy, through four complete masterpieces of the History of Philosophy (three in translation), compiled by Monte Ransome Johnson for students at UC San Diego.
The .pdf document, which is 672 pages, contains translations of Plato’s Gorgias, Lucretius’ On the Nature of Things, Descartes’ Discourse on the Method, and Hume’s Inquiry concerning Human Understanding.
All of the works are in the public domain and available at the internet archive. The title page and list of contents contains all the publication information, and instructions for how to properly cite and refer to the works.