The right book format depends entirely on what you plan to do with the file next. EPUB, PDF, and DOCX each preserve different things β and each loses something when you convert away from it. Knowing the trade-offs before you switch saves you from an unpleasant surprise after the fact.
Reading on a phone or e-reader: choose EPUB
EPUB is the best format for e-readers. Fonts, margins, and line spacing adjust to fit any screen, and the text reflows so you never have to scroll sideways. PDF, by contrast, locks the page exactly as it was laid out β useful when illustrations or precise page numbering matter, but awkward on a small screen where you end up zooming in and out constantly. If you just want to sit down and read, EPUB is the right call.
Editing or preparing for layout: choose DOCX
When you need to make changes to the text, DOCX is the practical choice. Modern word processors handle it cleanly: headings stay as headings, paragraphs stay editable, and the structure holds together. The older DOC format opens in most editors, but compatibility is patchier β if a book arrived as DOC, it's worth converting it to DOCX straight away rather than running into format quirks mid-edit. ODT is a reasonable alternative if you work in LibreOffice or a similar environment.
Only the text matters: choose TXT or Markdown
TXT and Markdown strip everything down to bare text. They open in any program, load instantly, and work well for searching, note-taking, or feeding content into another tool. All formatting disappears β headings, tables, illustrations β so this is only the right choice when structure genuinely doesn't matter and portability does.
What gets lost in conversion
Every format change involves a trade-off, and it helps to know what to expect. When converting to PDF, text and structure are preserved but the pages are re-laid out β the original page breaks won't match. In EPUB, fixed page references disappear entirely, because the format has no concept of pages. Convert to TXT and all formatting goes: headings, bullet points, tables, everything. The rule of thumb is to pick the format that fits your next step, not the one you're used to. After any conversion, open the result and check the key elements: headings, tables, and any images or illustrations.
Converting without the manual work
Once you've decided on a format, there's no need to copy text by hand or reassemble chapters. With SonikaAI's file converter, you upload the book, pick the target format, and the converted file is ready in your account. If you also want to translate the book or turn it into an audio version in the same workflow, that's available too β without stitching several separate services together. For a closer look at what each format handles during translation, the post on translating, narrating, and converting documents with SonikaAI covers the practical differences in more detail. To try it with your own file, try for free β no card needed to get started.