How can I configure Plasma activities so that evince does not show up on all activities, but only on the current activity I am using?

That should be the default behavior.

If you right-click on the title-bar and use the Activities submenu to move it to a specific Activity, does it respect that?
Do you have any window rules which might be coming into play under System Settings -> Window Behavior -> Window Rules?

airdrik wrote:That should be the default behavior.

If you right-click on the title-bar and use the Activities submenu to move it to a specific Activity, does it respect that?
Do you have any window rules which might be coming into play under System Settings -> Window Behavior -> Window Rules?

My situation is the following: any Gnome application, like evince, gedit, gnome-calendar, that I start on KDE/Plasma, put itself on all Activities. The windows of such Gnome applications do not have an activities submeu when right-clicking on the title-bar and I've read somewhere, that applications have to "register" with KDE/Plasma (?) somehow in order to work properly with the Activities.

My question: is there any tweek or can I reconfigure KDE/Plasma so that Gnome applications work well with Activities? Is there a way to patch and recompile Gnome applications so that they behave well with KDE/Plasma's activities.

Note that the Gnome applications work perfectly fine, but I don't want them to spread to all activities. Of course I could start using okular instead of evince, but I really prefer evince.

Are they using their own titlebars (a.k.a. CSD, client-side decorations)? I recall reading something about applications which did this didn't work with KDE's activities. Instead you may need to disable CSD for them to behave properly.
This askubuntu post suggests installing a 3rd-party utility called gtk3-nocsd in order to disable CSD for apps using gtk3's gtkHeaderBar.
I believe there may have been an option in System Settings -> Window Behavior for telling KWin not to respect CSD.