PPT "note taking" overlay app?

[D_o_S]

Hi guys,

does any app exist that would allow me to take notes over pdf files/ppt? I mean like I'd click on the slide where I want to place the note, then I could type the note, and it would stay there when I open the ppt/pdf in the future? A lot of stuff I do is listening to lecturers, and I already have their presentation... it is most usefull to write notes into it, rather than rewrite the whole slide + their additional info...

Thanks,