How to yellow highlight differences of two tex documents automatically in LaTex

Question

I want to compare two different tex files, say old.tex and new.tex, by just yellow highlighting the different places in the new.tex automatically.

I tried two ways but not exactly what I want.

1. Use package soul and command \hl in new.tex. This is ok but it is a manual process and very time-consuming.
2. Run latexdiff old.tex new.tex > diff.tex in the PowerShell, and then compile diff.tex in LaTex. This is automatical, but would highlight the diffrent places in both old.tex and new.tex (contain delete and add notations). Besides, it is not yellow highlight.

Really hope someone can help me, thanks very much in advance.

Answer 1

Let's suppose you have these two files, respectively old.tex and new.tex:

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\begin{document}
    This is the old document.
This an old line.

We will remove this line.

\end{document}

and

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\begin{document}
    This is the new document.
Esta es una nueva línea.

\end{document}

If you run latexdiff old.tex new.tex > differences.tex you will have a file which once compiled gives you:

Ok, now open the new file. Around the beginning of it, you'll find:

 %DIF PREAMBLE
\providecommand{\DIFadd}[1]{{\protect\color{blue}\uwave{#1}}} %DIF PREAMBLE
\providecommand{\DIFdel}[1]{{\protect\color{red}\sout{#1}}}                      %DIF PREAMBLE

The two commands that mark the "new" text and the "deleted" text are \DIFadd and \DIFdel. Change them to this:

\usepackage{soulutf8}
\providecommand{\DIFadd}[1]{{\protect\hl{#1}}} %highlight
\providecommand{\DIFdel}[1]{}                  %do not show deleted

Then compile it, you'll have:

Notice a couple of things:

1. I use soulutf8 because of this: French accents in \hl from soul package
2. latexdiff has a very complex task to do, and it's not 100% reliable or easy to use; but in plain things it works quite well.
3. I have no idea on how \hl will work on large texts or figure or paragraphs...