There are some who published only in paper or hardback books, others who have added audio-books to their editions, and then there are some who only publish in ebook format. Whether you publish in Smashwords, iBooks, or even Kindle editions all books really should be converted over and available to anyone who would like to read them. Each of these companies has a great distribution network and offers to send you stories out to them at a price – a percentage of your royalties. However, there is another format you might want to consider and that is offering your old, out-of-print stories in Acrobat Reader PDF format and offer them for sale on your very own website.
Even with the other eBook sellers out there, you will be doing the bulk of the marketing to get your books sold. If you have a big backlist of stories you published before and did not convert over to eBook format yet and retained those rights you might as well do it yourself. That way you can keep 100% of your royalties. The process is very simple with a couple of tools like Microsoft Office Word or even the Free Version called Open Office you can format your book inside the program and either “Save As” or “Print As” the book in PDF. That is the most universally accepted format for books around the world.
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If you pay for the Adobe DC software (monthly or yearly subscription) you will be able to encrypt the book against printing or editing of any kind. There are free software helpers for website owners, especially WORDPRESS plugins, that you can use to sell your digital files. You just connect your online store pages to your Paypal account (which is also free to sign-up) which protects your banking information. Once the customer pays for the eBook they will either be directed to a download page or emailed that information. This will all depend on which software packages your use.