All three formats store books and documents, but each one is designed for a different use. Choosing well avoids tiny pages on the phone, heavy files and broken formatting.
EPUB: for reading on screen
EPUB is the standard format for digital books. The text adapts to the screen: you change the font, the size and the spacing, and the book reflows. It is the best format for novels and any long reading on the Kindle, the phone or the tablet. It is also the format Libtro uses to translate and narrate.
PDF: for keeping the page the same
PDF freezes the page exactly as it was laid out. It is great for printing, official documents and material where the position of things matters: comics, sheet music, cookbooks with photos, workbooks with diagrams. On small screens, however, it forces you to zoom. For continuous reading, converting to EPUB is usually better.
DOCX: for editing
DOCX is the format of Word and compatible editors (LibreOffice, Google Docs). It is for those who still need to change the text: reviewing, commenting, formatting. For reading, it is less practical than EPUB, but the Kindle accepts DOCX by email.
Quick summary
- I'm going to read on the Kindle or the phone: EPUB.
- I'm going to print or need the page to look identical: PDF.
- I'm going to edit the text: DOCX.
In Libtro you convert between the three in Actions → Convert. The original file stays in your library.