Debian xarchiver "Failed to execute child process "ar" (No such file or directory)"

I have Debian 9 and Xfce. am trying to install a commercial program given as a .deb -ending file. When I double click on the file, it opens a window titled "(filename.deb) - Xarchiver 0.5.4" and on top of that a pop-up error message Can't run the archiver executable: Failed to execute child process "ar" (No such file or directory) Is ar a command I'm missing? I tried on a terminal sudo apt-get install ar and the response is E: Unable to locate package ar A similar problem seems to be in https://unix.stackexchange.com/q/199774/344355 but their context is KDE, not Xfce.