qpdf: join pdfs into a single pdf file

qpdf --empty --pages *.pdf -- joined.pdf

LibreOffice freezes on logo

Disable opengl: SAL_DISABLE_OPENCL=1 libreoffice

Linux: Copy all files from subdirectories into one folder

find zfiles/* -type f -mindepth 2 -print0 | xargs -0 cp -t ./sub1