Why won’t my ebook open?

There are only about five reasons a book refuses to open, and almost nobody tells you which one you have. You get “unsupported file format” or nothing at all, and you are left guessing whether the problem is the file, the app, or you.

It is almost never you.

This is the full list, in order of how often it actually happens, with a way to tell each one apart. If you would rather not read the whole thing, you can drop the file into the checker and be told which case you are in — it reads the first four kilobytes in your own browser and nothing is uploaded.

1. It has DRM

This is the big one, and the most misunderstood.

DRM — digital rights management — means the text inside the file is encrypted. Not hidden, not awkwardly formatted: mathematically scrambled, with the key held by the shop that sold it to you. Their app has the key. Nothing else does.

So when a reader refuses a book you legally bought, it is usually not being difficult. It genuinely cannot see the words.

How to tell. Kindle files carry an encryption flag in their header, a few bytes into the file, and any tool can read it without decrypting anything. If you bought the book from the Kindle Store, assume it is set. The checker reads that flag and will tell you outright.

What you can do. Not much to the file itself, and this site will not help you strip it — but the useful thing to know is that a great deal of what you can buy has no DRM at all:

• Books you send yourself. Anything you email through Send to Kindle is a personal document, and personal documents are not encrypted. Those open anywhere.
• Publishers who sell DRM-free by policy: Tor, Baen, No Starch, Pragmatic Bookshelf, Manning, Leanpub, most university presses.
• Standard Ebooks and Project Gutenberg, which are free, out of copyright, and beautifully typeset.
• Humble Bundle and itch.io book bundles, which are usually DRM-free.

If you plan to keep your library for decades, that list is worth more than any reader app.

2. The extension is lying

A filename is a label somebody typed. The contents are a fact. They disagree more often than you would think, and the mismatch is invisible until something refuses to open.

The most common version: an .epub that is really a folder of scanned page images. An EPUB is a zip archive. So is a comic book archive. So is a folder of photographs. Some conversion tools produce the second and name it like the first, and the result looks like a book right up until a reader opens it and finds no text — only pictures of text.

The others you will meet:

• A DjVu renamed .pdf. DjVu is a scanned-image format from the 1990s; renaming it does not make it a PDF.
• A .pdb that could be a Mobipocket book, a Palm address book, or half a dozen other things — the extension was shared by everything Palm ever made.
• A .zip that somebody hoped was a book.

How to tell. Every real format leaves a signature in its opening bytes — %PDF, PK for anything zip-shaped, a Palm database header for Kindle books. That signature cannot be renamed. Reading it is the only reliable way to know what you have.

3. It is a picture of a book, not a book

A scanned PDF contains no text. It contains photographs of pages. Your eyes do the reading; the file does not know any words at all.

This catches people out because a scanned PDF looks completely normal — you can see the words, you can zoom in, you can print it. But select a paragraph and you will find there is nothing to select, and search will find nothing either.

How to tell. Try to select a sentence. If you cannot, or if you get a blue box over the whole page instead of a line of highlighted words, it is images.

What you can do. Run it through OCR — optical character recognition — which looks at the pictures and produces text. Most phones now do this natively (Live Text on iPhone, Google Lens on Android), and Acrobat, ABBYY and the free ocrmypdf all do it properly for whole documents. The output is a normal PDF with a text layer, and that opens everywhere.

A note worth having: OCR is never perfect, and the errors it makes are strange ones — rn becomes m, l becomes 1. That is tolerable in normal reading, where context repairs it before you notice. It is much less tolerable in a paced reader showing one word at a time, where the wrong word is the only thing on screen.

4. The format is dead

Some formats simply have no reader left. Not “no good reader” — none.

• LIT (Microsoft Reader) — discontinued in 2011, and most files are DRM-protected anyway.
• LRF / LRX (Sony Reader) — discontinued, and LRX is encrypted.
• RB (Rocket eBook) — a format from 1998.
• TCR, SNB, PDB in its stranger variants.
• KFX, which is current, but is Amazon’s encrypted format and cannot be read by anything else.

What you can do. Calibre converts almost all of these to EPUB, free, on your own machine. It is the single most useful piece of software an ebook reader can own, and it has been maintained continuously since 2006.

The exception is anything encrypted. Calibre converts formats; it does not break encryption.

5. It was never a document

Worth saying because it happens constantly: an audiobook is not a book. An .m4b is a recording — there is no text inside it to show you. A photograph of a page is a photograph. A .csv will technically open and will be miserable to read one word at a time.

None of these are mistakes anybody should feel silly about. “I have a book, in a file, why won’t the book app open it” is a completely reasonable expectation, and the honest answer is just that the words are not in there.

The two-minute version

Checking without guessing

Everything above can be determined from a file’s first few kilobytes — the format signature, the DRM flag, whether a zip holds text or images. No uploading, no waiting, no account.

That is what the checker does. Drop a file, and it tells you what it actually is rather than what its name claims, whether it carries DRM, and what to do if it will not open. If it will open, it will tell you how many words and chapters it has and roughly how long it will take you to read.

It runs entirely inside your browser. The simplest way to prove that is to turn off your wifi and try it — it still works, because there is nothing for it to reach.

And if it opens

Then you can read it. ReadKinetic opens thirty-nine formats — EPUB, PDF, Kindle, FictionBook, Word, OpenDocument, PowerPoint, LaTeX, Markdown, subtitles and plain text among them — and shows them one word at a time at a pace you set, keeping your place and your chapters, without uploading anything and without an account.

The books you own should open. When they do not, you deserve to know why.