In reply to David.

I know that Tesseract released version 4.0 since I wrote this post, which I'd assume is an API-breaking change to some degree or another. Given that PyPDFOCR hasn't been updated in three or four years, it's not all that surprising that it's broken. Depending on your use case, I'd recommend checking out ocrmypdf as an alternative; I wrote a bit about that in my updated version of this post.