Drop in a chord chart or a lead sheet (sheet music with chord names), or paste a chart with the chords sitting above the words. Tidy the chord placement on the right, then download a .cho that Songbook Pro and OnSong can transpose. The ChordPro on the right is yours to edit before you download. Sheet music can also be redrawn in another key.
Put the cursor in or just after a chord and hold Option with the arrow keys to walk it one character at a time until it sits on the right syllable. Typing in the right pane works normally too.
Once you edit the ChordPro, it stops following the left pane so your work is safe. Rebuild regenerates it from the source and discards those edits.
A dropped PDF is read straight from its text layer and the columns are rebuilt, which holds the chords over their words better than copying and pasting does. Odd spacing still happens on cramped charts — fix it in the left pane and the right one follows. A scan, photo or screenshot is read like a photo instead (that part needs internet the first time) and marked for you to check.
Sheet music is read as music rather than as text: each chord is matched to the syllable it is sung on, a word split over two lines is joined back up, and when there are two lines of words (two verses, or two languages) you can pick which to keep. Below the panes the page itself can be redrawn in any key — Nearest keeps the tune in the same range, Up and Down choose the octave. This works on PDFs saved straight from notation software; a scanned page is only a picture.
Nothing leaves your machine. The PDF reader is built into this page, so apart from photo reading it works with the wifi off.
Section names are written as {comment: Chorus}. Don't add {start_of_chorus} underneath one as well: Songbook Pro then shows the heading twice.