Create the structure:

sudo mkdir /usr/share/doc/l4akb
sudo mkdir /usr/share/doc/l4akb/latex

Copy a document

Let's say we take a good latex copyleft book like Peter Flynn's "A beginner’s introduction to typesetting with LATEX"

sudo cp ~/beginlatex-3.6.pdf /usr/share/doc/l4akb/latex/beginlatex.pdf

Set permissions

Don't forget to set the right file permissions to assure that other people can read the document

sudo chmod 644 /usr/share/doc/l4akb/latex/beginlatex.pdf

Create the control file

Change to the doc-base directory and copy an existent control file and adapt it for your needs.

Note: To avoid errors do not make any manual line breaks!

cd /usr/share/doc-base
sudo cp dc l4a-latex-beginnerdoc
sudo nano l4a-latex-beginnerdoc

Content of the control file

Document: l4a-latex-beginnerdoc
Title: A beginner’s introduction to typesetting with LATEX
Author: Peter Flynn
Abstract: This book originally accompanied a 2-day course on using the LATEX typesetting system. It has been extensively revised and updated and can now be used for self-study or in the classroom. It is aimed at users of Linux, Macintosh, or Microsoft Windows but it can be used with LATEX systems on any platform.
Section: Apps/Tex

Format: PDF
Files: /usr/share/doc/l4akb/latex/beginlatex.pdf

Make the document visible

For this reason you have to "install" ( to register) the document.

sudo install-docs -i l4a-latex-beginnerdoc