One can use MD5 or plain text diff to see differences in PDF files. If that's not enough, here's how to use [diff-pdf](https://vslavik.github.io/diff-pdf/) which knows how to diff based on appearance or words:

* ```brew install diff-pdf```
* edit your `~/.gitconfig` to add this:

```
[difftool "diffpdf"]
  cmd = diff-pdf --view \"$LOCAL\" \"$REMOTE\"
```

* then use with:

```
git difftool --tool=diffpdf your_pdf_file.pdf
```

I suspect there's maybe some way to force always using a specific difftool for files with a specific extension; in the mean time I'm just using a bash function for this.

Also useful in `.bash_profile`:

```
function git_diff_pdf {
  yes | git difftool --tool=diffpdf $1
}
```

then you can use it like:

```
git_diff_pdf your_pdf_file.pdf
```