Here's a very basic plugin that can search in attachments.
At this point it only supports PDF attachments with text, i.e. it does not have OCR capabilities.
In its current state it's not intended for production use as it has some serious flaws. It won't mess with your data but:
- it will re-index all attachments at startup
- there's no guarantee it'd extract all text from PDFs
- it may slow Joplin down
- and as you can see the UI is horrendous: I could not figure out how to resize the window with results to fit the content, and I also wanted to have clickable links to open a note containing the resource, but I'm not sure if it's possible at the moment.
Putting it out there so that maybe someone can get an inspiration from it.
I'll probably take a break from Joplin plugins for some time, although I may eventually update this plugin.