What I have found.

I had been using Pdf files with the UnReal Book until I found the OnSong App for my IPad.
Once a PDF file is made there can be no changes. Any change that is made requires redoing the process.

With OnSong you can:

1-Change the fonts
2-Add a new thought without redoing the process.
3-OnSong can handle PDF files much like the UnReal Book
4-Combine files
5-Transpose instantly
6-Add add information in color to the song.
7-Change the color of the chords above the lyrics so the page is easier to reed
And more.

John C.