When I create a "combined pdf" from several files, using Acrobat Pro DC, the first page of the resulting pdf portfolio "forces" one to download Acrobat Reader. I use a Mac and my preferred pdf reader is Preview so I do not then have Acrobat Reader installed on my Mac any longer. Why am I forced to download Reader?
PDF Portfolios are special sort of PDF files which can be viewed best in Adobe Acrobat and Reader only. Other PDF viewers do not have the capability to render PDF portfolios.
Hope this helps!