Materia culturalis:
If you're interested in learning more about the Roman language and culture, I'd be happy to provide you with some general information or recommend some resources.
A free scanned PDF is a terrible user experience. You cannot search it reliably. The margins are cut off. The images are black-and-white blobs. A $20 used copy from AbeBooks is infinitely more pleasant.
For a structured learning experience, consider combining free PDF resources with more traditional educational materials or courses. Many universities and educational institutions offer courses on Latin and Roman civilization, which can provide a comprehensive and engaging learning experience.
As mentioned, the work is in the public domain. A search for the PDF should yield results from reputable sources. When downloading, look for the following to ensure you have the complete text: