Resolved with:
- searching for posts with images by selecting filter Includes image(s) in section Only return topics/posts that… - Search posts with images by dmacjam · Pull Request #4917 · discourse/discourse · GitHub
- searching for posts which contain files with explicit file extensions by querying
<keywords> filetype:pdf- FEATURE: Search posts by filetype by dmacjam · Pull Request #4958 · discourse/discourse · GitHub