The reason you may not be viewing your PDF proof properly is a result of a setting in your Adobe Acrobat (or Adobe Reader) needs to be adjusted.
I believe when creating your artwork, the artist made a multi-channel Adobe Photoshop document that has CMYK plus Spot channels. In order to preview this properly and see the content you need to turn on your in Acrobat Reader.
is turned off by default (both in and the free ) and must be activated in the preferences of each application.
Open up (or ) then go to (Mac) or menu then PC).
Next, select from the list.
In the Use pull-down menu, choose .