8 thoughts on “Some EPUB Identifier Best Practices

  1. John

    This removes the obfuscation and will allow you to keep your ISBN as the unique-identifier. A nice side benefit of this fix is that, because Kobo does not currently support font obfuscation, your EPUB file will display properly on Kobo devices.

    What about font licences?

    We have had this problem recently and had to acquire a licence for fonts which come pre-installed on Mac computers. Indeed their licence doesn’t cover epub and Kindle according to our legal team—they have spent weeks on this issue, which is ridiculous—and we had to purchase a specific ebook licence online.

    Best part of this story is that we had to obfuscate the fonts and subset them using software the foundry has specifically developed… and something InDesign does in backstage.

    In other words, I’d advise people to behave very carefully when it comes to embedding fonts because breaking the user agreement can be as simple and fast as embedding the whole unsubsetted font in your epub file.

  2. Joshua Tallent

    John, that is a great comment, and one I should have remembered to mention in my article. Yes, it is very important to know about your font licenses and be sure you are not breaking them by undoing the obfuscation. Thanks!

  3. Keith Stevenson

    Hi and thanks for a great article.

    You mention a problem with embedded fonts if you change the uid from the one indesign generates. In indesign you can choose not to embed fonts when you export to epub, which I do regularly. Would this avoid the problem?


  4. Joshua Tallent


    Choosing to not embed fonts will keep you from having the problem of obfuscated fonts, but it will not keep you from having the issue with the unique-identifier being set as a UUID. I’d still recommend replacing the UUID with your ISBN in the metadata.


  5. Brian Phillips

    Thanks for this info!
    Is there a preferred application for applying obfuscation/subsetting to fonts, so it can be applied outside of the inDesign export?

    Also, has Adobe indicated, to your knowledge, that they’re on top of little issues like this?

  6. Chris Benge

    Thanks for this, Joshua. I’ve always thought the ISBN number ought to be the primary go-to option for unique id of an InDesign file. What I’m not clear about from your post, however, is precisely how to phrase the content of the MetaData’s Identifier field to comply with requirements. Should it read: “urn:uuid:xxxxxxxxxxxxx”? or “urn:uuid:ISBNxxxxxxxxxxxxx”? Or do we not need anything more than the ISBN number code?

  7. Darko Martinovic

    Unique Identifier is needed as you can have multiple packages in the same publication with different isbns … and also multiple versions of the same book published in their own publications. So as a reading system developer , we have to know by some identifier that we are dealing with a same work, in different language, or in different display format etc.



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