Completed request 7808634 was for pdf preview, which of course works in ProtonMail Windows app, and also in ProtonDrive Android.

But in ProtonMail Android, although I've updated to latest version, the "Open With" for pdf attachments doesn't offer me an integrated Proton pdf viewer.
Only 3rd party ones, including Google Drive and Dropbox... giving me a quick workflow to save recieved pdfs into Dropbox. But of course I'd like my default cloud to be ProtonDrive!