Melisearch is integrated into Linkwarden. That’s about my extent of knowledge.

And have you found a way to have it search within PDFs?

I did look at melisearch briefly to see if I could use search engine databases in creating my own search engine just as a project because I’ve often toyed with the idea of having my own search engine, but it seemed a bit over my head. Smithsonian Libraries publish some of those databases.

I use Karakeep which uses Mellisearch as a part of its stack

Paperless ngx seems to support fulltext search of PDF’s, in addition to other document types.

It’s part of Bar Assistant stack. Haven’t got into it outside of it

Yep. I have an instance I self-host to power a “cookbooks -> scanner -> images -> OCR -> indexed search” tool I built for myself. The whole thing is pretty much just a few bash scripts thinly wired into a Meilisearch instance, but the utility is helpful when looking for a recipe from my collection.