How it works
Output = the characters stored in the PDF's text layer, page by page in page order | A page with no text layer (a scanned image) contributes nothing — extraction creates no text that the file does not already contain
Your file is processed entirely in your browser and never uploaded: the PDF is opened on your own device, its text layer is read page by page, and the extracted text is shown for copying or offered as a plain-text download. Nothing reaches a server, and the tool works offline once the page has loaded. What is extracted is exactly what the file stores: a born-digital PDF — written by a word processor, a report tool, a browser's print-to-PDF — carries its words as character data with positions, and that data is what you get back.
The limit must be stated plainly, because it is the most common disappointment with tools of this kind: a scanned PDF is a photograph of pages inside a PDF wrapper. It has no text layer, so there is nothing to extract, and this tool will return little or nothing from it. No OCR is performed — the tool does not look at the page images and guess at letters, and it does not claim to. If your PDF came from a scanner or a phone camera, the words are pictures; text recognition for those belongs to a dedicated OCR application, after which the recognised text can come back here for cleaning with the text tools.
Even from a good text layer, extraction is faithful rather than beautiful. Multi-column pages can read across columns rather than down them, because the layer stores positioned fragments and the reading order is reconstructed from positions; hyphenated line-breaks in justified text may survive as hyphens in the output; tables arrive as spaced runs of words, not as a grid. The extraction is the raw material — word counts, searching, quoting, feeding into the Word Counter or a diff — and for those jobs raw and complete beats formatted and partial.