I have two versions (A4 size) of a document: `new.pdf`

and `old.pdf`

.

I'd like to share with co-authors a pdf with pages side by side, so should be easy to compare the changes in the output.

Here there is a partial solution which works well **only if the files have the same number of pages**.

An extension of that partial solution is proposed and makes use of `\pdflastximagepages`

to compute the number of pages of a previous inserted pdf file. So this number can be used for the loop.

Since my pdf files could have **different numbers of pages**, the solutions cited above don't work.

So, my idea is:

**1.** compute the number of pages for both files.

```
\sbox0{\includegraphics{new.pdf}}
\edef\PagesA{\number\pdflastximagepages}
\sbox1{\includegraphics{old.pdf}}
\edef\PagesB{\number\pdflastximagepages}
```

**2.** define the numbers `\Min=min(\PagesA,\PagesB)`

and `\Max=max(\PagesA,\PagesB)`

**3.** from `1`

to `\Min`

insert pages from both files using

```
\foreach\n in{1,...,\Min}{
\includepdfmerge[nup=2x1]{new.pdf,\n,old.pdf,\n}
}
```

**4.** finally, test if `\Min=\PagesA`

or `\Min=\PagesB`

.

**4.1** if `\Min=\PagesA`

then use

```
\foreach\n in{\Min+1,...,\Max}{
\includepdfmerge[nup=2x1]{old.pdf,\n} % old is on the right hand side
}
```

**4.2** if `\Min=\PagesB`

then use

```
\foreach\n in{\Min+1,...,\Max}{
\includepdfmerge[nup=2x1]{new.pdf,\n} % new is on the left hand side
}
```

**My question is:** how to implement (4)?

**M(W)E**

```
\documentclass{report}
\usepackage[landscape,margin=0pt,a3paper]{geometry}
\usepackage{pdfpages,pgffor}
\begin{document}
\pagestyle{empty}
\sbox0{\includegraphics{new.pdf}}
\edef\PagesA{\number\pdflastximagepages}
\sbox1{\includegraphics{old.pdf}}
\edef\PagesB{\number\pdflastximagepages}
%\edef\Min{}
%\edef\Max{}
\foreach\n in{1,...,\Min}{
\includepdfmerge[nup=2x1]{new.pdf,\n,old.pdf,\n}
}
\foreach\n in{\Min+1,...,\Max}{
%% test here to decide if new or old should be used
\includepdfmerge[nup=2x1]{??.pdf,\n}
}
\end{document}
```

## Best Answer

A similar solution than the one mentioned before in the comments. The differences are:

Here the MWE: