Given a working directory and a folder c with encrypted PDFs, use qpdf, basename and a bash loop:
for f in c/*.pdf; do qpdf --password=<password> --decrypt $f "$(basename -s .pdf $f).pdf"; done
Given a working directory and a folder c with encrypted PDFs, use qpdf, basename and a bash loop:
for f in c/*.pdf; do qpdf --password=<password> --decrypt $f "$(basename -s .pdf $f).pdf"; done