I use DT2G at work to maintain manuals, work orders, sign offs etc and it has simplified my life! There’s a but, I have yet to find a simple way to select and email two or more PDFs at a time. Currently I export them to Dropbox, attach them with Spark and then after sending delete them from Dropbox. What am I missing?
You’re not missing anything… except that functionality. 
It’s currently not possible to do. However, we do have a feature request in place. Cheers!