Comment by eigenvalue

I made a site recently that works pretty well for this for a lot of sample scanned PDFs I tried, you might get good results:

https://fixmydocuments.com/

I also made a simple iOS app that basically just uses the built in OCR functionality on iPhones and automatically applies it to all the pages of a PDF. It won’t preserve formatting, but it’s quite accurate in terms of OCR:

https://apps.apple.com/us/app/super-pdf-ocr/id6479674248