I agree with Gene. The most likely problem is that this PDF so happens to be an image-scanned PDF without any text layer associated with it. They are out there by the millions, particularly for older scanned PDF files.
Either try NVDA OCR or download the file and use whatever OCR processing you may prefer to add a text layer to the entire document. The latter is easier if the document is long, at least to me, or if it's something you intend to refer to later.
Brian - Windows 10 Pro, 64-Bit, Version 20H2, Build 19042
Any idiot can face a crisis. It's the day-to-day living that wears you out.
~ Anton Chekhov