Most public and university libraries provide free remote access to the Oxford English Dictionary Online . You can simply log in using your library card number.
Searching for a free PDF download of the complete Oxford English Dictionary (OED) often leads to unreliable or unauthorized third-party sites. Because the full OED spans 20 volumes, it is not typically distributed as a single PDF.
Some official apps allow you to download the database for offline use without needing a PDF file. Digital Resources
Access while away from institution - Oxford English Dictionary