Photoshop CC not responding when opening a 2MB PDF file
I'm using PhotoShop CC 2014 under Yosemite on a 2012 MacBook Pro. I'm not seeing an issue, even testing with a 5MB PDF.

One thing to consider is that the PDF file is corrupt. To check this, try loading some alternative PDFs into PhotoShop.

Instead of drag-dropping the PDF onto the Dock icon, you can also try either of the following:


Right-click the PDF, then choose Open with >> PhotoShop.
With PhotoShop open, drag-drop the PDF from the Finder window to the PhotoShop window.