A print interior serves a physical book
Print layout fixes the placement of words and images on pages. The file must be prepared for the chosen size, platform and production requirements. A print interior and a print cover are separate deliverables, so confirm both when discussing a project.
EPUB usually serves an adaptable reading experience
Many text-led ebooks use reflowable EPUB, where text adapts to the reading device and the reader’s settings. A book with complex fixed page relationships may need a different approach. Discuss the content and intended store before choosing an export.
A screen PDF preserves the page
PDF is useful when the layout needs to remain fixed, including many workbooks, handouts and direct-sale resources. Readers may need to zoom on small screens, so check how the file will be used rather than assuming one page design works equally well everywhere.
A fillable PDF adds interaction
A fillable PDF can provide fields for typed responses, but behaviour varies between PDF viewers. Test it in the applications your readers are likely to use. A screen PDF with blank lines does not automatically become a fillable file.
Request the right combination
Tell your designer where the book will be published, how it will be sold and whether people will write, type or simply read. Then list the needed formats explicitly in the scope, including any editable source files.