EPUB vs PDF: what an EPUB file is, and how Chrome opens it

Updated 22 October 2026

Almost every ebook you download is an EPUB, and almost every browser pretends it doesn't exist. Here is why the format was invented, what makes it different from a PDF, and what actually happens when you open one in Chrome.

Why EPUB exists

A PDF is a photograph of a printed page. It was designed in the 1990s so that a document looks the same everywhere, which is exactly what you want for a contract or a datasheet, and exactly what you don't want for a novel on a phone. Zoom a PDF to a readable size on a small screen and you scroll left and right across every line. So, what people did? EPUB.

EPUB was created in 2007 to fix that. Instead of fixing the page, it stores the text and lets the device lay it out. Make the font bigger, turn the phone sideways, switch to a wider window, and the text reflows into new pages. The name is short for "electronic publication", e and pub; the format is maintained today by the W3C, the same body that maintains the web's own standards, which is a clue to what it is underneath.

What is inside an .epub file

The EPUB is ZIP archive with a fixed layout inside. Rename a book to .zip and open it and you will find:

• the chapters, as ordinary web pages (XHTML) with a stylesheet;
• the images and, sometimes, the fonts the publisher chose;
• a "package" file that lists every part in reading order, with the title, author and language;
• a table of contents;
• for some shop-bought books, an encryption.xml that says which parts are locked (that is the DRM).

So an EPUB is, in effect, a small website in a box. That is why it can reflow, why a reader can search it and highlight it, and why it is usually a few hundred kilobytes where the same book as a PDF is several megabytes.

EPUB vs PDF, side by side

The honest summary: EPUB is for reading prose on any screen; PDF is for documents whose layout matters more than the reader's comfort. A textbook full of diagrams is better as a PDF. A novel is better as an EPUB. Converting one into the other is possible with Calibre, but converting a PDF into an EPUB usually produces broken paragraphs, and an EPUB into a PDF freezes it at one page size.

How Chrome opens them

PDF: Chrome has had a built-in PDF viewer since 2010. Click a PDF link and it opens in the tab.

EPUB: Chrome has no EPUB reader, and never has had one. Click an EPUB link, or open an EPUB file, and Chrome downloads it to your Downloads folder and stops. Nothing is wrong with the file; the browser simply does not know what to do with it. (Microsoft Edge could read EPUB until 2019, when Microsoft removed the feature.)

To read the EPUB, something else has to take over:

• A Chrome extension. Readkave, the extension this site is about, opens the EPUB in a browser tab: drop the file into its library, or switch on "Open ebook files in Readkave" so that Chrome opens EPUB links instead of downloading them. It works offline and keeps the book on your computer.
• A web app. Google Play Books lets you upload an EPUB to your Google account and read it on play.google.com/books. That needs the account and the upload, and the book then lives on Google's servers.
• A desktop program. Calibre (which also converts formats), Thorium Reader and Apple Books on a Mac all read EPUB. The file opens outside the browser.
• Your phone. Google Play Books, Apple Books and Moon+ Reader read EPUB on Android and iPhone. Chrome on a phone cannot run extensions, so there is no browser-only way there.

Opening an EPUB in Chrome, step by step

1. Install Readkave from the Chrome Web Store and click its icon. The library opens in a tab.
2. Drag the EPUB onto the page, or click "Choose files". The book opens with real pages, a table of contents and your position remembered.
3. Optional: in the library settings, switch on "Open ebook files in Readkave". From then on, an EPUB link opens in the reader instead of landing in Downloads. For files you double-click on your computer, Chrome also needs "Allow access to file URLs" switched on for the extension; the help page shows where.

When an EPUB won't open

• "Protected by DRM." Books from Kobo, Google Play Books and most libraries are locked to the app they came from. No browser reader can open them, Readkave included; read them in that app. Books from Project Gutenberg, Standard Ebooks, Humble Bundle and your own files have no DRM and open fine.
• The file is a web page. Some download links hand you a sign-in page saved as book.epub. Open the link in Chrome, download the real file, then open that.
• The file is damaged. A download that stopped early produces a ZIP with its end missing. Download it again.
• It is really a PDF. Some sites name every download .epub. If the first characters of the file are %PDF, it is a PDF: rename it and Chrome opens it itself.

Which should you keep?

If you have the choice at download time, take the EPUB for anything you will read start to finish, and the PDF for anything you will look things up in or print. If you only have the PDF of a novel, converting it in Calibre is worth trying, but check the first chapter for broken line breaks before you commit to it. If you only have the EPUB and need a PDF to print, Calibre's conversion gives you a clean one at the page size you choose.

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