Spell check statistics (number of spelling errors)

I’ve downloaded the dictionaries and everything, but I have a document about which I only want to know the number of orthography errors/non-existing words. It’s a text from OCR and I want to quickly assess its quality.

File > Property > Statistics doesn’t have anything; Tools > Word count neither; Tools > Spell checker don’t offer any suitable option even in “Other”; Tools > Spell checker options neither.

I’m using LibreOffice

How is this outdated?