I have just made my Concrete Handbook for Artists: Technical Notes for Small-scale Objects available as a PDF download from my web site. The 12MB digital file is available for $15. I'm confident that once people see and read the PDF version of the book many will want the "real" version in its original paperback form. I'm also hoping the PDF file will get wider distribution of the book.
One of the big advantages of a PDF file is that it is searchable on your computer. I searched for the word "metakaolin" for example, and Acrobat Reader found it 26 times in the digital file, including the definition and sources of supply. In the paperback copy you can use the index, but the PDF version is much faster. You can also print out the whole book, but this is 135 pages, so I don't imagine too many people will do that. It's at that point where I would personally buy the paperback edition. And the PDF file doesn't include the color cover. I had to cut that to keep the file size down to a reasonable amount. Other positives for the digital format? No shipping costs, which for the paperback is now $3 in Canada, $7 to the US, and $13 to all other countries. And no paper is used, just ones and zeros.
If you're interested, here's a link directly to the PDF order page:
You might be wondering what got me started on all this. Someone emailed from Chile with a request. "Do you have a PDF version of the book? The post office here is so slow and unreliable." That got me thinking about the process so I gave the first digital copy to him.