I use calibri font family (cyrillic). While exporting a book as PDF for any version (1.5, 1.4 I tried) calibri is successfully added to the window of embedded fonts, but the resulting PDF is uneditable. Subset checkbox in Fonts settings is unchecked.
Solved by installing version 1.5.8. and exporting the file from it. Old version (Stable) seems unable to do that.