PDF trouble
How do you save multiple pdf files into one file?
Preview or Acrobat are the first two program that come to mind
in Preview (free with OS X) you can drag multiple PDF's into the thumbnail window and arrange them to make a multiple page PDF
Apple changed the way it works from previous versions (or there is a bug in the Yosemite version) where the source images or text need to be PDF to begin with, you can't assemble a multi page PDF from jpg's or png's, etc - at least a bunch of us on this forum couldn't - your source files need to start as PDF's.