Turn sheet music into note names you can read at a glance: C, D, E, F♯ and so on, measure by measure, with the lyrics underneath.
A PDF or photo is a picture of notes, so it first has to be read by a music-recognition program (OMR). Any of these turns it into a MusicXML file you can open here. Recognition is good on clean printed music and makes mistakes on handwriting or blurry photos, so glance over the result.
.mxl). From a terminal: Audiveris -batch -export -output out/ song.pdf. Get Audiverispip install oemer, then oemer photo.jpg writes a .musicxml next to the photo.