Qubes comes with a "Convert to trusted PDF" out of the box. Joanna Rutkowska explained how it works under the hood pretty nicely[1]. The tldr is that it is very thorough. With Qubes it is convenient too.
I used Qubes to open the application mails and their attachments and converted the interesting ones to trusted PDFs which I then forwarded to the relevant people. All further communication was only with the trusted versions.
[1] https://blog.invisiblethings.org/2013/02/21/converting-untru...