I believe when you scanned the document you saved as image (jpg, jpeg or png) format. unfortunately, thou I know about free tools like PDF Creator and PrimoPDF, I doubt whether they can merge separate docs into one, honestly I never tried with them, but I know with NitroPDF Professional or Acrobat Professional you can merge your scans into one single pdf doc. You can always give the two freeware I mentioned a try, else buy a copy of either Nitro Pro or Acrobat Pro...