When you order from us and the score is transposable you will get two files in the download. One is a pdf if you just want to print it out. The other is an RMS file. The RMS file is a file that is understood by our SheetMusicNow Viewer application. If you open the file in the application you can play back MIDI and transpose and extract lyrics.
You can see a full online manual of the viewer product here.
You can download the viewer product from here.