Apple Preview app has inbuilt OCR even for really old scan PDFs
This was a pleasant surprise for me.
I have a few PDFs containing music scans, probably of books that are 40 years old. The scans are probably photocopies of the originals, they are that bad. I was going to wait until I had access to a PC with Adobe Acrobat installed because I wanted to run its OCR and resave those PDFs with the text embedded.
But then I happened to open one of these PDFs on my MacBook Air and, just for fun, typed a word into the search box. It immediately began searching through the PDF and showed me where the word appeared.
Of course, this is live and will be lost the moment you close the PDF. You need to export the PDF again through Preview with 'text embed' turned on if you want the OCR text to be permanently saved.
But this was such a cool surprise, especially since Preview is free on Apple devices. I really appreciate what Apple has done with this.