1. Get some decent image editing software (e.g. the gimp for mac
2. Open/import pdf in/into editing software
3. select single card
4. crop to selection
5. save as jpg
6. repeat until done..
If you don't know how to download and install software: Sorry for you.
If you don't know how to open/import/select/crop/save: Learn how to do it (start by reading the gimp tutorials