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One advantage of always adding additionally a bookmark file as well is, that you can use it in any proper pdf reader for searching. Additionally you can import the song indexes in any proper music reader. Most work is creating the list of song names and page numbers for an excisting book with say 100-1000 songs. Once you've done that creating a bookmark file and adding it to the pdf book is a matter of minutes. Then you have a pdf book everybody can use in any reader.

It should be remembered that also adding some correct properties in a pdf will be useful. Several  readers will also use the properties which for instance contain the album name, keywords and a composer name (only useful if all songs in the book belong to the same  composers/creators) etc.
Properties are also hidden info in a pdf file which can be read and edited using several free downloadable exe files.