I NEED TO KNOW HOW TO RESTORE IT TI OPEN ACROBAT NOT ILLUSTRATOR WHEN I CLICK ON A PDF FILE THAT COMES IN VIA E-MAIL
It's an operating system issue.
Select Acrobat instead of Illustrator
select for all files of these type, not just the one file to make it the default.
Does that work?
I'm having this same issue. I've tried your suggestion and it works a couple of times, but somehow resets to Illustrator as the default for opening all PDF files. Even when I export a PDF from InDesign and select "view PDF after exporting", it launches Illustrator.
When I choose Open with, I also select the "Change All" button.
Can you show a screen shot of the Finder or Windows File Explorer and show what you are doing when you make this change? Do you have permissions on the folder the PDF is being saved to? Can you get it to change at all, or does it fail immediately?
This is an OS related problem. At some stage you assigned Illustrator as the preferred .pdf handler. You need to reassign Acrobat as the tool to use. You need to give the OS and version, so that you can get targeted advice for correcting this.