DoxyModel.pm: it is a Perl module with information about the structure
of DoxyDocs.pm files.  It is used by Perl scripts that process the
output generated by the Perl backend.
   
doxydocs-latex.pl: it is a Perl script which uses DoxyModel.pm and a
generated DoxyDocs.pm to create the file doxydocs.tex. This file
contains the documentation, this time in "TeX" format.  doxydocs.tex,
however, can't been directly LaTeX'ed.

doxydocs-latex.ltx: this is the LaTeX file which is LaTeX'ed to
generate the PDF or DVI documentation.  It includes doxydocs.tex,
generated by doxydocs-latex.pl above, and doxytemplate.tex, generated
by doxytemplate-latex.pl -- see below.  This file is intended to be
customized by users if they want to modify the format of the PDF or
DVI output.

doxytemplate-latex.pl: this is a Perl script which uses DoxyModel.pm
to generate a doxytemplate.tex TeX file.  This file is included by   
doxydocs-latex.ltx to maintain the compatibility with future versions
of Doxygen; i.e. a customized doxydocs-latex.ltx should work with the
output generated by future versions of Doxygen as long as it includes
an updated doxydocs.tex.

So what do you do to test my backend?

1. You apply perlgen.diff and rebuild Doxygen.
2. You save DoxyModel.pm, doxydocs-latex.pl, doxytemplate-latex.pl and
doxydocs-latex.ltx to your test directory.
3. You run doxytemplate-latex.pl to generate doxytemplate.tex.
4. You generate DoxyDocs.pm by running Doxygen on the test code.  (You
must enable the GENERATE_PERL option in your Doxyfile).
5. You run doxydocs-latex.pl to generate doxydocs.tex from
DoxyDocs.pm.
6. You run pdflatex on doxydocs-latex.ltx to generate
doxydocs-latex.pdf from doxydocs.tex and doxytemplate.tex.

If you want to regenerate the PDF output after modifying the test code
you only need to do the steps from 4 on.

I also attach a main.h file I've used to test my backend and the
corresponding main.pdf file I've generated from it.