A song is nothing more than a list of MusicPages. The pages can appear in any order, and can appear multiple times. If there's a repeat on page 4 going back to page 2, it is recommended to add pages "2, 3, 4" twice in a row so you can page-down every time you get to the end of a page and not worry about going back to find the repeat on page 2 while performing. You would then end up with the following page sequence: 1, 2, 3, 4, 2, 3, 4, 5, 6.
Song files have the extension
.song.xml on disk and they store the full path
to the MusicPages making up the song.
Since PDF files can be (much) slower to load than JPGs, it is possible to convert the song pages from PDF to JPG by using "Convert to JPG" from the Song context menu, or the menu bar. This only works on songs where all the pages come from a single PDF file. When using this menu option, you will be asked to choose a directory to hold the JPG images. It's a good idea to save them to a new separate directory. You will also have the option to move the original song and PDF to the new directory. The new song will be added right after the PDF-based song in the current PlayList and have "JPG" at the end of its name.
PDF files can also be converted directly to song files by following the instructions to ConvertFromPdf. Starting with version 2.50, PDF files can be read directly by opening them just like a regular graphic file. A dialog box will prompt for the range of pages to use out of the PDF.