An EPUB file itself consists of several other files, namely:
- (X)HTML and CSS resources
- images
- fonts
- etc.
Some retailers do not accept EPUB files whose names, and whose component names, contain spaces or special characters. It is especially important to avoid the following elements in the file names:
- accents;
- apostrophes;
- spaces.
For example, the file name demo page test.html is invalid and the fille will be rejected, whereas a file named demo_page_test.html will be accepted without error.