By default, eWriter eBooks contain both the viewer program and the book itself in a single EXE file. This is great for single eBook, but it's a little wasteful if you're installing multiple eWriter books as help files on a single user's computer. Then you have a copy of the viewer in every file, and every file also has to be a signed EXE. It also makes it more difficult to distribute updated versions, because making an EXE file available for download is more problematic than a plain data file.
To get around these problems, eWriter can also publish the viewer and book components separately. Then you just install the viewer once, and you can add as many separate eWriter books as you like, all viewed by the same viewer program. And when you want to distribute updates you just need to make the data-only book files available.
When you create a separate eWriter viewer it is actually a complete single-file eWriter eBook, containing both the viewer and a book part of its own. If it is opened on its own without a reference to a separate book file it will just display its own integrated book. So when you create your viewer for your books, it's a good idea to do it with some basic information that you won't want to change all that often.
In the examples we use the extension ".ebk" for the separate book files. This works fine but it is not required. You can use any extension you like as long as it is not .exe and not associated with any other programs on Windows. For example, the extension .ewriter also works fine.