Combining PDF files

[Diane35781996a1b2]

I am trying to use the COMBINE FILES for multiple PDFS and on my new macbook it only shows up as file list (see screenshot below).

I cannot figure out how to have them all merged into 1 document.  On my old macbook I did this all the time and it would create a PDF of all.  When I click open document, nothing happens.  Any ideas?

Please help.

[Abambo]

What is the Acrobat version? 

[Diane35781996a1b2]

See screenshot.  Could I be missing a plug in?