I just updated to Photoshop CC 2014, and now I can't open PDFs which came from my scanner. I scanned these files using OS X Mavericks built-in Image Capture tool, at 300 dpi, "text" mode, which I believe is 1 bit color. I never had this problem in the past with Photoshop CC.
We would need to see an example PDF file to know what could be going wrong with the file.