Are you trying to open PDFs on (a) a Windows or Mac computer or (b) a mobile device (e.g. iPad/iPhone, Android tablet/phone)?
Would you please describe what happens when you try to open a PDF? Do you see a blank page or an error message?
"website" -- That says you are accessing via a web browser. Today many of these default to an "in-house" PDF viewer that is only minimally capable.
So, always save PDFs to the local machine/device and have Adobe Acrobat Reader DC (mobile or desktop version) installed to open/view.
Another issue may be that the "PDFs" are actually forms created by LiveCycle. These are forms of an XML flavor (XFA) that are "wrapped" in PDF (think taco eh).
If this is the case then these can only be viewed with Reader or Acrobat.