A Correspondent observes that PDFs and digital booklets are no longer lodged in the "Music" library but in the "Books" library. Thus he laments that he is unable to access these books alongside the music tracks while browsing the "Music" library. While book-type tracks and music tracks can reside in the same playlist, yes, they do belong to different libraries. But creating a separate playlist for every album with a PDF or digital booklet doesn't seem very efficient.
I used Change Hidden iTunes Preferences to toggle the visibility of the "Library" library playlist. In the pic below it is listed atop the other library playlists. In the old days, this was the main library playlist and listed everything in the library. Well, it still does. When the "Library" is available, you can use the Column Browser to access an entire Album, which will include any associated booklet (providing the Artist/Album tags correspond correctly):
(The yellow highlight over the booklet is an artistic representation.)