If you're looking for a way to setup a menu on the left hand side with the ability to nest sub-menus you might wish to look into the menu plugin.
Its nice and in theory so far you should be able to nest all the PDF files you wish under any one directory. Same will go for TXT and which ever files are native to a browser...
You might have to manually place these files on your server or better yet upload them with the file management plugin. Once they're ready simply link to the documents using the menu plugin in the fashion you wish.
Its pretty versatile and all plugins work great for me so far... Good luck
---Victor B. Gonzalez
Victor B. Gonzalez -
http://aeonserv.com