Document Viewer - i.e. PDF reader is currently managed by Evince “Document Viewer”.
In progress upstream is a GTK4 port and it will be a libadwaita based app. Unknown when it will land - but currently has GNOME 43 milestone associated with it - so Ubuntu 22.10.
Thus looking at alternatives in the archive - most PDF readers seem to be Qt based - okular which is well maintained is a KDE based app - so not suitable.
Thus atril - which is managed by the Mate Desktop team is perhaps the best alternative (?) - disappointingly there is a huge backlog of issues and progress is relatively slow unfortunately.
So open to ideas here - I’ll mark atril as a replacement for evince for the moment