[Plugin: wp-mpdf] mpdf plugin changing characters in my post

Hi,
After enabling mdpf, some characters are not correctly parsed in the posts on my blog.
Characters such as double quotes (and other characters) are replaced by a question mark…
Returns (br) are replaced with �, and so on

When I deactivate the plugin, the problem disappears…

What is wrong here

http://ww.wp.xz.cn/extend/plugins/wp-mpdf/