Another idea: Put the free online pdf version after a quarter. That means the premium customers buy the printed version (or even a DRM'd pdf), and later it is released as free version.<br><br>If the pdf is released in both versions, it should have watermark to identify whether this is a premium version or a free version.<br>
<br>Another idea borrowed from the Economy Editions of certain books: The premium version is full color, and the free version is B/W (only some images may be color).<br><br>The general idea is to add value to the premium version, so that people who CAN pay would prefer them.<br>
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