I am unable to open .pdf documents in my email. What has happened? Did something change in the last update?

Upon opening some emails containing a .pdf document I am unable to

opem these documents my iPhone 6 plus. Upon clicking on the attachment the screen shows a quick image of the words (.pdf) but then goes black. When I click on the black screen it shows a white screen and no image. I've experienced this with several emails now. Has the new software disabled the ability to open a .pdf or have I gotten a bug? I have re-started my phone to see if that would remedy it. The problem still exists.