Anyone can tell me why this " don't prevent that filenames with spaces get interpreted as arguments?
I think it is the second
find /home/user/pdfs/ocr -type f \( -iname "*.pdf" -and -not -iname "*_ocr.pdf" \) | while read file ; do ocrmypdf -q -l deu+eng --rotate-pages --rotate-pages-threshold 8 -c -s "$file" /home/user/pdfs/ocr_fertig/$(basename "$file" ".pdf")_ocr.pdf && rm "$file" ; done