Why some EPUBs can't be converted
DRM, .acsm files, fixed-layout comics and non-Latin scripts. What each one looks like, why it stops the conversion, and what you can do about it.
Updated August 8, 2026
Most EPUBs convert without incident. Four kinds do not, and it is worth knowing which is which, because two of them are fixable and two are not.
DRM-protected books
What you see: the converter opens the file, then tells you the book is DRM-protected and stops.
What is happening: the text inside the EPUB is encrypted. The file is a
perfectly valid container, but the chapters are ciphertext, and there is nothing in
them to typeset. The converter checks for this before doing any work, looking for
the encryption.xml or rights.xml file that shop-bought books carry. The
alternative is grinding through a long book to hand you three hundred pages of
noise.
Why we stop rather than continue: we do not remove DRM. That is a deliberate line, not an oversight, and it is not going to move.
What you can do: check whether a DRM-free copy exists. A surprising number of publishers sell one directly even when the big retailers do not:
- Standard Ebooks and Project Gutenberg — public-domain literature, beautifully produced, never encrypted.
- Publishers’ own shops — Verso, Tor, No Starch, Manning, Pragmatic Bookshelf and many others sell DRM-free.
- itch.io, StoryBundle, Humble Bundle — DRM-free by default.
- Your library, sometimes. Borrowed books are encrypted, but many library systems also carry public-domain titles that are not.
If you bought the book and only have an encrypted copy, the shop that sold it to you is the place to ask.
.acsm files
What you see: the converter says the file is an Adobe download token rather than a book.
What is happening: an .acsm is a few kilobytes of XML. It is not a book at
all; it is a voucher that tells Adobe Digital Editions which book to fetch and how
to unlock it. People download one expecting an ebook and end up with a file their
computer does not know how to open.
What you can do: open the .acsm in Adobe Digital Editions, which will download
the actual EPUB. That EPUB will normally be DRM-protected; see above.
Fixed-layout books
What you see: the converter warns you that this is a fixed-layout EPUB and that the text options will not do anything.
What is happening: comics, graphic novels, children’s picture books, some cookbooks and most magazines are published as fixed-layout EPUBs, where each “page” is a single full-page image with the text baked into the picture. There is no text in the file to reflow, and therefore none to set.
What you get: the images, one to a page. That is a perfectly reasonable PDF of a comic, and for a comic it may be exactly what you wanted. It is just not typesetting, and no page size or type setting will change anything.
Books in non-Latin scripts
What you see: a warning that some or most of the characters cannot be set, with a few examples.
What is happening: we set the text in the fonts already built into every PDF reader: Times, Helvetica and Courier. That is why nothing has to be downloaded to use the converter, why it works with the network unplugged, and why the finished PDF is usually smaller than the EPUB that produced it: the file carries no font data at all.
Those fonts cover the Latin alphabet and its accents, which is more than people expect. French, German, Spanish, Italian, Polish, Czech, Turkish, Icelandic, Vietnamese and the Nordic languages all set correctly, diacritics included. What they do not cover is Greek, Cyrillic, Hebrew, Arabic, Devanagari, or any of the CJK scripts. Those characters come out as question marks.
Two different warnings: if a handful of characters are affected, say a Greek letter in a maths footnote, you will be told and can reasonably ignore it. If most of the book is affected, the warning says so more firmly, because converting it would be two minutes of waiting for a document you cannot read.
What you can do: nothing here, honestly. This one is a real limitation of the approach rather than a setting. A converter that embedded a full Unicode font could handle it, at the cost of shipping several megabytes of font data to every visitor and producing much larger PDFs.
Everything else
If the converter opens your book and produces something odd rather than refusing it, that is a different situation and probably fixable. How it works covers what the converter is good and bad at, and the options that usually help.