latexdiff is a Perl script that compares two latex files and marks
up significant differences between them (i.e. a diff for latex files).

Various options are available for visual markup using standard latex
packages such as "color.sty". Changes not directly affecting visible
text, for example in formatting commands, are still marked in
the latex source.

A rudimentary revision facilility is provided by another Perl script,
latexrevise, which accepts or rejects all changes.  Manual
editing of the difference file can be used to override this default
behaviour and accept or reject selected changes only. There are also
scripts to handle multiple-file documents, and files under version
control.

WWW: http://www.ctan.org/tex-archive/support/latexdiff