When trying to attach a pdf, I get this error message.
I do run in the latest chrome browser in incognito mode with paperpile activated (otherwise the icon would not show up)
What am I doing wrong (seperate window is meh 
You can’t use Paperpile in incognito mode. Paperpile needs access to the internal file system of Chrome and that’s not possible in incognito mode.
If you want to manage multiple google accounts in separate windows we recommend to use Chrome profiles.