Filing this so that others who update a patch version of the repo and wonder why some lines broke will be able to find it:

In 1.27.6, all errors were moved to PyPDF2.errors (in commit 1f0fbf3)

So if you were previously importing PdfReadError from PyPDF2.utils and are no longer able to, you need to change your import to get PdfReadError from PyPDF2.errors.