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PDFs use a fixed layout that doesn't scale with the device or window size, so they're not as friendly for smaller screens. Some people do read PDFs on some phones, though -- some screens are prett...
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#3: Attribution notice added
Source: https://writers.stackexchange.com/a/21635 License name: CC BY-SA 3.0 License URL: https://creativecommons.org/licenses/by-sa/3.0/
#2: Initial revision
PDFs use a fixed layout that doesn't scale with the device or window size, so they're not as friendly for smaller screens. Some people _do_ read PDFs on some phones, though -- some screens are pretty big and some people have good eyes and can read the small page. Also, some of your readers might be using tablets rather than phones. However, I wouldn't make the QR code link to a PDF _or_ an ebook. I'd make it link to a _landing page_ -- a web page where you can include links to whatever download formats you like and say a little about your book. (These cards sound like marketing materials, so bridge that gap between "somebody handed me this QR code" and "I want to read this book".) If your needs change (e.g. new formats) you can just update that page. Someday it might even contain links to the sequel. For one example of landing pages, look at the per-book pages in the [Baen Free Library](http://www.baen.com/catalog/category/view/s/free-library/id/2012).