A quick Google search for the exact keyword phrase reveals a fragmented landscape. Many websites claim to offer a free PDF of the dictionary, but users must tread carefully.
Purchase a used physical copy of the "Longman Basic Picture Dictionary" or the "Word by Word" series (often confused with Longman) for $5–$10. If you own the physical book, scanning it for (creating your own PDF) is generally considered fair use, provided you do not distribute it. the longman picture dictionary american english pdf