Steps to reproduce:
Test Browser: IE11, Chrome 45, FF 40
1. Login as admin user
2. Create any site,
3. Create any folder
3. Navigate to folder and upload any file. (for example: *.doc) in the site document library
4. open document Details page for the doc.
Expected: preview should be displayed correctly.
Actual: Preview is not displayed: the following message is displayed:
"Could not load PDF content"
Ref: Screen shot attached
Note: This issue seems to be inconsistent and not always reproducible.