Import ebook: "subtitles can't be used"

I am trying to import an ebook and I get the error “subtitles can’t be used” and can’t do it. I’ve tried in PDF, TXT and then copied all the text into a whole new PDF, but nothing works. Does anyone know what’s up?

Please check your email Chris, I replied you there. I need you to send me that PDF file so that I can test it on my end and try to figure out what’s going on. Thanks.

Sometimes you get that error when there is DRM protection on the book. Not sure if that is the case here, but I received that error on some things I imported. Once I removed the DRM, the book imported as expected.