Spell Check a PDF in Preview?

You can only spell and grammar check text that you input. Since Preview is not a PDF editor, you can only perform spelling and grammar check on text annotations, either during input, or afterward by selecting the text annotation.

You can copy and paste the text into another document and run spell check from there. I know, it's not the same as running it right in the source document, but AFAIK that is the best you can do with reviewing it in Preview.

Even if you could copy/paste the text into TextEdit, or a word processor, you would still need a PDF editor to make changes in the original PDF.

As there a several PDF editors in the Mac App Store, it is reasonably close to 0% that Apple is going to transform Preview into a PDF editor. Can't speak for Apple future product directions.

Very true that you can not edit the PDF document from wherever you paste it. However, the cut & paste does indeed work in a number of programs and will allow you to comment back to the original PDF author regarding required or preferred edits. I know cut & paste works, I use it regularly to copy from PDFs. I used to have Adobe Acrobat Pro but no longer use it. It would allow spell check and edits to some documents (as long as they weren't password protected).

I am not disputing the ability to copy/paste text from a PDF into another application — provided that the PDF security permits it. Communicating edits to the original PDF author (if known), via another application, is out of scope to the OP's original question.

All very true. My suggestion was simply offered as a work-around. It's about all one can do from the Preview app in that instance.