The tool
Open a PDF from this Mac. It is read here, changed here, and saved here; nothing is sent anywhere while you work.
The text this file shows
Open a file to list its lines.
Change run
The page
The sheet is the page as it is drawn. The text plate is the same page with only its words left on it.
The text layer, as a file
Every line this file shows, in reading order. Copy it, or save it as a text file.
A scanned page
Read the words off the page image on the right, then keep them as text or add them to the page as a second layer. Your document is not sent anywhere to read it — the character data is part of this page.
The words go under the picture, in a layer of their own. Text already on the page is not touched.