Make terminal command use both CPU cores
Depending on the number of PDFs you have to process and the nature of the tasks, you may consider installing GNU parallel in brew.

GNU parallel allows you to execute several jobs concurrently. Example:

parallel ::: yes &gt; /dev/null yes &gt; /dev/null


An example script (containing small errors e.g. line 13 should start with find instead of ind!) how to use parallel and ghostscript can be found here: Quick shell script for parallel OCR on PDFs using ghostscript and tesseract

Please also check the extensive man pages of parallel.