This is possible with a third-party plug-in from Evermap called AutoPortfolio, but only if you "convert" the existing portfolio created through Outlook to a standard or "flat" PDF. During this process, you can also specifiy the output sort order or tightly define the content to be included in the conversion, exclude certain file extensions, etc. It works very well.
Disclosure: I have no affiliation of any kind with Evermap, but did address the use of several of their products in my book, "The PDF Litigation Guide."
Hope that helps!
Jason Covey
PDF Litigation Solutions, LLC
www.pdflitigationguide.com