You can legally access Merriam-Webster's Advanced Learner's English Dictionary

also provides a way to "borrow" digital copies of the dictionary for a set period. Merriam-Webster Website : While not a PDF, the official Merriam-Webster Learner's Dictionary

: The most reliable way to access the full content of the learner's dictionary is through the official Learner's Dictionary website Internet Archive : You can legally borrow a digital copy of the 2008 edition for limited periods through the Internet Archive Mobile Apps : Merriam-Webster offers a free version of their Dictionary App on Google Play