You need to know the chords, or have a chart of them, and enter them yourself in the Editor. iReal Pro cannot import a PDF, a MIDI file, or MusicXML and turn it into a chart.
Charts shared on the Forums follow a set of house conventions. Before you post one, read iReal Pro layout conventions and the iReal Pro glossary.
For the full guide, see Create a song on the iReal Pro website, and Edit a song for the Editor itself.