Sorry to hear about this. It still works for me. But I obtained it originally by Googling something like “Sierra 10.12.4 AND PDF problems”. It was close to the top of the list. (And thanks for the advice from the DT developers; I know that they’ve spent a lot of time devising and implementing workarounds for Sierra’s PDF issues. It’s not something that I as a decade-long Apple user have expected over that period.)
Hugh, thank you for the Google search term. I found this link:
Which pretty much answers my question with this final recommendation about whether to upgrade to 10.12.4:
“To answer those who have asked if they can now upgrade to Sierra, I’d have to say that if you rely heavily on apps built on top of PDFKit for viewing and manipulating non-trivial PDFs, it’s probably worth continuing to hold off. If you mostly just read PDFs in Preview, you likely won’t hit any stumbling blocks unless you work with large or encrypted PDFs.”