well there are "various" websites where you can get pdfs from, torrents etc. however if you plan to use them in kindle for example only books purchased FROM kindle (that say search) usually have a search feature, so while you can still import the pdfs in, its not very helpful in finding anything. epubs (dont work in the kindle app) seem to be a bit more advanced and have various capabilities including search but not many of the unsavory websites have them as widely available as pdfs.
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