Why does Lightning Source require an EPUB file?
Each of our 70 e-book retail & library partners has unique file requirements. A valid EPUB, created with our outlined specifications,¬ enables us to satisfy the requirements of each partner, getting your e-book where it belongs—on every device.
Can’t you just use my PDF?
The majority of e-retailers will not sell PDF files in their e-book stores. The EPUB format is the official standard of the IDPF (International Digital Publishing Forum) and is designed for reflowable content, meaning an EPUB reader can optimize text for a particular display device.
Can I just run my PDF through an EPUB converter?
Not all EPUBS are created alike. Most conversion services, particularly the free ones, have disclaimers that their conversion services are not suitable for a production environment. We highly encourage you to verify that the files created at each site will be suitable for a production or manufacturing environment and not for personal use only.
Is there a way to tell if my file is valid before I upload to Lightning Source?
Yes, we recommend running your file through IDPF’s free EPUBcheck Validator. It can be found at Please note the IDPF Validator can only accept files up to 10 MB.
Rejected IDPF EPUBcheck Validator
There are e-retailer specific requirements IDPF doesn’t check for built into Lightning Source to lessen the chance of rejection later in the process.
The IDPF EPUB Validator does not check to see if images have more than 3.2 million pixels, as it’s not wrong. Because this is something required by our e-retail partners, it was built into the Lightning Source requirements on the front end. Therefore, it is possible to pass IDPF validation, but still get rejected by Lightning Source.