When you add pdfWidget to .pro it gives following warning

Project MESSAGE: This project is using private headers and will therefore be tied to this specific Qt module build version.
Project MESSAGE: Running this project against other versions of the Qt modules may crash at any arbitrary point.
Project MESSAGE: This is not a bug, but a result of using Qt internals. You have been warned!

Attached patch solves it, but there likely other problem in other pri files like qt_lib_pdfquick.pri