When displaying a document from the Doc Lib in Webcenter, you may be getting the properties for the file but not the web preview.
If you have setup Webcenter and UCM/IBR following the documentation, you may be missing the PDF third party font path. If you don't set this up conversion to PDF may fail and pass through.
Go to IBR
login as weblogic and your password.
Click on Conversion Settings and the options button for OutsideIn Filter.
Input the path to TrueTypeFont.
In my case my linux didn't have the fonts. However some were included in the JRE of webcenter.
You can go to your middleware home and perform a Find -name fonts, in case you can't find them.
After including the setting documents preview correctly.
For power point slides ensure you had the Powerpoint slider ucm component before enabling the webcenter configure component. You can check by browsing dynamic conversion templates from UCM power user interface.