To display pdf previews in file field, I found out that pdf to image was a prerequisite to file field. Does pdf to image provide additional functionality to file entity by intent oder by accident?
See also the related issue for file entity at #2611650: When is pdf preview formatter available? →
Closed: works as designed
3.3
User interface
Not all content is available!
It's likely this issue predates Contrib.social: some issue and comment data are missing.