The trouble is that this isn’t a simple thing to do. Reading a PDF takes time, managing a very large number of them would require indexing, and if the text isn’t already in extractable form, it will require OCR.
Docfetcher, a very useful open source text searcher (in maintenance mode last I heard owing to maintainer’s lack of time) has the following in its FAQ:
Why are the DocFetcher installer and the other packages so large (> 30 MB)?
This is mainly due to the fact that DocFetcher is shipped with lots of built-in text extraction libraries, some of which are quite big. The worst offenders are the libraries for MS Office and PDF files. However, the developers of these libraries aren’t to blame here: The libraries have to be big because the respective file formats are immensely complex.
The whole point of plaintext and markdown is that it is quickly and easily read. PDFs are a whole extra world of processing requirements.
My suggestion for people who need to be able to do a native Obsidian search on this text would be to bulk extract the text outside of Obsidian and put it into separate files with links to the original PDF.