I think the PDFs are designed mostly to go to print? These aren't really targeted towards the general e-reader-owning demographic, but they're readable at zoom-to-fit size without squinting on my 13" MacBook.
Anyway, it might be worth suggesting to the author that a consistent single-page variant instead of the current double-page spreads would be a handier and more versatile option for the e-book freebie.
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