Hello,I need some help, I have a kindle HD and I have downloaded Adobe but when I try to download some if the story links, it says on my kindle downloading but then when I try to open file it says it can't be opened ,there is a icon next to it with a arrow pointing down and it says the file is PDF ,my other stories I can open have a PDF at the end of the description and says PDF to the left but the ones I can't open ( to the left have a arrow pointing down), can someone please help,Thanks