I use K-9 Mail and also the new betas. But I can 't find any way to print out email-messages or download them as PDF-files to the Android device. Please explain this topic detailed, our if actually not possible, please put this features to your agenda to implement in the final new version of K-9 Mail. Thank you.
Neither of these features are currently supported. Both are very low priority issues for me.
K-9 Mail supports sharing the email text to another app. Many printing apps support receiving shared text.
When viewing a message open the ‘send’ (sub)menu, then select ‘Share’.