There can be so many forms of the dictionary for offline use. I feel, PDF form of the dictionary is the worst form. There will be Devanagari text or other non-Roman text, besides Roman text. This, if converted to PDF, either makes the non-Roman text 'distorted/changed' if done in Unicode. If it is done with legacy code, it does not get 'distorted' after making PDF. But searching in it is very difficult/impossible.
PDF is only good for printing the file on paper. It is much better to have the dictionary in simple text, DOC, html, epub, as excel/Calc file for offline use. They all provide excellent search facility, which is a great facility for dictionaries. Also, one can convert these files in a number of ways and styles. The dictionary itself can be modified, arranged in a different order etc.
-- anunAd