What Is a PDF File?

PDF (Portable Document Format) is a file format that preserves a document’s exact layout — fonts, images, spacing, page breaks — so it looks identical no matter what device, operating system, or software opens it. That’s the entire point of the format: what you see is exactly what everyone else sees.

Why This Matters for Authors

Unlike EPUB or MOBI, which are reflowable (text adjusts to fit any screen size), a PDF is a fixed layout — every page looks exactly the same every time. This distinction is why PDF and EPUB serve different purposes in publishing:

• PDF is what most print-on-demand services (like Amazon KDP Print) require for your book’s interior file, since a printed page needs a fixed, exact layout.
• EPUB is what ebook retailers require, since ereaders and reading apps need to reflow text to fit different screen sizes and font preferences.

If you’re publishing both a print and ebook edition of the same book, you’ll typically end up needing both formats — a PDF for the print interior, and an EPUB for the ebook edition.

When You’ll Use a PDF as an Author

• Formatting your print interior for KDP Print, IngramSpark, or another print-on-demand service — see our guide to print-on-demand book sizing for the trim sizes these files need to match.
• Sharing a manuscript for review with an editor, beta reader, or formatter, since a PDF displays identically regardless of what software they open it with.
• Some ebook platforms, like Pothi, which sell books in PDF format specifically — see our guide to selling on Pothi for an example.

If You Need to Edit a PDF

See our full guide to editing a PDF if you need to make changes to a PDF you don’t have the original source file for.