How to Extract Text from a Scanned PDF
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Not all PDFs contain 'text' in the same sense. A PDF exported directly from Word, Google Docs, or a web page contains an actual text layer — every character is stored as character data, which is why you can select and copy it, and why a text-extraction tool can pull it out instantly and accurately. A scanned PDF, on the other hand, is really just a sequence of images, one per page, that happen to look like a document. There's no text data in the file at all — just pixels arranged to resemble letters.
This distinction is exactly why 'extract text' and OCR are two different tools rather than one. Text extraction reads an existing text layer, which is fast and essentially perfectly accurate, since it's just reading data that's already there. OCR (optical character recognition) has to analyze the image, identify shapes that look like characters, and guess what each one is — which is inherently slower and introduces the possibility of misreads, especially with unusual fonts, low scan quality, or handwriting.
A quick way to tell which situation you're in: try selecting text in the PDF with your cursor in a normal PDF viewer. If you can select and highlight individual words, it has a real text layer and plain extraction will work perfectly. If clicking and dragging just selects the whole page like an image, it's a scan, and you'll need OCR instead.
For OCR results, always proofread the output, particularly for numbers, proper nouns, and anything in a table — these are the areas where character recognition most commonly makes mistakes, since there's less surrounding context for the algorithm to use to guess a likely correct word.