Hi carolyn_aus,
Welcome to the HP Support Forums! :) I understand when trying to print to your HP ENVY 4500 from your Mac or iPad, it only prints half the page and then stops and you have to manually pull the paper out. I would like you to follow the steps listed below:
1. Reset the Printing System, please be aware that this will delete all print settings and pending print jobs.
2. Go into your 'Printers & Scanners' and click on the '+' and choose 'Add another Printer or Scanner'
3. Choose your Envy 4500 and where it says 'USE' change it to the HP Photosmart Envy 4500 Series.
Please let me know if you are now able to print a full document, I will watch for your reply.
Thank you,