The ODE is legally sold as an eBook and PDF-like file. The OED is not.
The search for is a search for a ghost. The file you want—a single, searchable, up-to-date, offline copy of the most comprehensive dictionary in human history—does not exist for a simple reason: the English language is not a static document, and neither is the OED. oxford english dictionary.pdf
One of the most fascinating aspects of the OED’s history is the "Reader" program. Realizing that no single team could read every book ever published, Murray put out a call for volunteers. He asked readers to find quotations that illustrated the usage of specific words. The ODE is legally sold as an eBook and PDF-like file