Copy and paste from a PDF reader gives you mush, and gives you nothing at all on a scan, with no way to tell whether the document or the gesture failed. Here, we say which.
What it does not do: We return the text as the document carries it: words hyphenated at the end of a line stay hyphenated, columns are not untangled, tables are not rebuilt as tables. Guessing at those things means being wrong in silence, and text that looks clean but is not is worse than raw text. A scanned page carries no text at all: there is no character recognition here, and there will not be, since it would need a library of several megabytes fetched from somewhere else, which this site forbids itself.
Nothing is uploaded. Cut your network connection once this page has loaded: the tool keeps working. How to check it yourself.