How can I avoid this new icon on portfolio advising to use Adobe?

If you are the recipient of the PDF, you can't. That's a PDF Porfolio "cover sheet" that displays when then PDF viewer can't display the PDF as the author intended. It's not new. If you are the author and you don't want that to be displayed for your users, either encourage then to install Adobe Reader or don't create PDF Portfolios and instead combine documents into a single PDF. 

Hey there!

Looking at the screenshot shared above, it seems you have been getting suggetions to download .pdf file supporting software, Adobe Acrobat/Reader. Do you use any other 3rd party software to view pdfs? 

You can download Adobe Reader for viewing pdfs, as its a free app. That may would remove the suggetsion box. Else, there should be a action button something like "do not show this message" or "ignore message".

Thanks,

Akanchha