This is copied from the "enhancement" thread.  Please make comments here.
 
I found my favorite format, easily made with my software, is a pdf published by my WordPerfect with 4x6 page size and 14 point text.
 
 
Anyway, in my WordPerfect, I use the "Headings" which provide the "links" when I "publish" the pdf with the proper settings.  
 
Well, I was trying multi level headings, Heading 1 for the book title and heading 2 for Chapters, and I decided to try Heading 3 for some subunits.  When I published the document to pdf and read it on my PEZ I was pleasantly surprised.
 
On the "Catalog" page, the Heading 1 shows up with an icon beside it.  When I choose that level, the subheading then open up, like the + and - in the folder options in Windows.  When I choose again, the subheadings close up.  
The first picture is the file, NLT Matthew (Christian Bible), then I show the Catalog page shown when I press button 7.  It shows Matthew with an icon.  I press number 1 and get the subheading of the Chapter 1.  I pressed its number and get the next level of subheadings. (sorry, I loaded them in a different order)
Oops,  my granddaughter got in there 
 
AJ