Are you aware of the fact that PDF can be anything between clean text-based LaTeX content and scanned graphical images, to just name two of the extremes of each

Are you aware of the fact that PDF can be anything between clean text-based LaTeX content and scanned graphical images, to just name two of the extremes of each possibility and not taking into consideration the immense variety possible in between? Unless you restrict your ambitions to a clearly defined type of PDF this mission is supposedly impossible. Have a look at https://en.wikipedia.org/wiki/PDF https://en.wikipedia.org/wiki/PDF to get an idea what kind of input data you are actually dealing with. PDF is a wonderful display output container at the end of the publishing chain, but nothing you'd ever desire as input for further textual manipulation.