Downloading Adobe Digital Editions to Kindle Fire HDX

I got my Kindle a few months ago and up until a couple of weeks ago I have had no problem downloading ebooks through Kindle, but now they say I cannot download PDF or ASCM files. I was on "Mayday" with Amazon for several hours but they were not able to help me. The site I troed to download the books from told me to install Adobe Digital Editions or Aldiko, and I have had no success with either. Can someone please offer me a suggestion? I'm totally frustrated. Thanks in advance.