Cannot open any pdf, says it is encrypted, which it is not.

This is kubuntu-19.10, Libreoffice Version: Build ID: 1:6.3.5~rc2-0ubuntu0.19.10.1~lo1, downloaded from ubuntu ppa “ eoan/main amd64 Packages”.

Attempting to open ANY pdf file gives the error “This PDF file is encrypted and can’t be opened.”.
They are not encrypted, other programs can open them. This has been happening over the last several updates. There are workarounds, but the problem needs solving (or a reason why it can’t be…).

Same problem. Even trying to open with Draw PDFs generated/exported by LibreOffice itself, the error occurs. Using LibreOffice (x64) on Windows 10.