I am now using imac, and want to export several PDFs as JPEG format. I have tried Preview, but not worked well for me, any other free solutions.

I googled online and find Mac Automator can convert PDF to JPG for me, if anyone has similar needs, you can try:
1. Launch Automator in Finder>Application.
2. Click on the Automator to run it, then choose “Workflow”.
3. In the Library column, click on “Files&Folders”, then drag “Ask for Finder Items” to the right column;
In the Library column, click on “PDFs”, then drag “Render PDF Pages as Images” to the right column;
In the Library column, click on “Files&Folders”, then drag “Move Finder Items” to the right column;
4. Click on the “Run” icon on the top right and locate PDFs that need to convert to JPG
5. You will find the JPEG files in your designated location. If you want to convert another PDF to JPG with Automator, click “Run” icon and choose the file for conversion.


tutorial source: https://www.cisdem.com/resource/how-to-convert-pdf-jpg-mac.html