Change Adope Reader Page Size

Thank you all for the many answers.  Much of the language is above my head, but will study and try.  Also, one person asked for a copy of the page in question.  It is the "cover page" and is one page with back,spine,cover within one flat page.  Will try to attach a copy and perhaps give better understanding.  I created this cover (and the inside pages of my book) with Microsoft Publisher 2007 in my Microsoft XP program and moved it to Microsoft Publisher 2010 when I had to add Microsoft 10 to my computers.  Size is (left page) 6" wide x 9" long, (center binder) 1/2" wide x 9" long and (right page) 6" wide by 9" long. Full size, one page, 12 1/2" wide and 9" long.  Need to save this to .pdf at this full size for sending to KDP.

Again, huge thanks to all of you responding.  I have been creating this book for 7 years now, my original books (3 of them) were published by Create Space and never had a problem.  Create Space sold out to KDP (Kindle Direct Publishing), this is the first book I am trying to publish since losing Create Space and it has been a nightmare.