While a full, free PDF of the Holman Illustrated Bible Dictionary may not exist legally, there are several legitimate ways to access its content without spending a fortune.
Even if you find a file, it is likely a low-resolution scan. Images will be blurry, maps unreadable, and text may suffer from OCR (optical character recognition) errors—defeating the purpose of an illustrated dictionary.
If you are a serious student of the Bible, owning a physical or official digital copy is a worthwhile investment. The is often preferred because the high-quality color plates and maps are easier to browse than in a scrolling PDF format.