Problem
When you check-in PDF files on Mac desktop clients the thumbnail for the asset is not generated and shows you a blank image as the thumbnail.
Affected Platforms
MAC OS (10.8) and above
Cause
from OS X Mountain Lion (10.8), Apple dropped dedicated support for X11.app, with users directed to the open source XQuartz project (to which it contributes) instead
Solution
Install Xquartz from the website below