# Convert documents to PDF
libreoffice --headless --convert-to pdf *.pptx

# Save them to a different directory?
libreoffice --headless --convert-to pdf *.docx --outdir ~/docs/

# Convert files nested inside folders?
# This uses sharkdp/fd, you could use GNU find, xargs etc.
fd -e doc -e docx -x libreoffice --headless --convert-to pdf --outdir {//} {}