We were running Acrobat CS2 and Photoshop CS2 but have recently upgraded to Acrobat Pro DC. Now any PDF created or modified using Acrobat Pro DC will not import into Photoshop CS2.
It throws the following error "Could not complete your request because this is not an Adobe Photoshop PDF image"
It isn't too surprising that a 10 year old app cannot handle files made with an app with 10 years of changes. Are you able to open them in Photoshop CC2015?