I’ve auto-updated Avast from version 7 to 8. I’d like to know where the setup.exe of version 8 temporary resides, so that I could copy the setup to another PC. I’ve limited bandwidth, so I don’t want to re-download again.
Does anyone know??
As far as I’m aware there isn’t one.
If you downloaded then ran the install the file should be in your download folder.
If you installed via the GUI, DavidR is probably right.
I have learned to download “then” install. That way I still have the file in my download folder.
I then transfer a copy to a USB stick for future use. I only do this for “final” releases and not for betas. 
Once in a blue moon I’ve run into an installer that’s a stickler for neatness, and includes deleting itself plus any temp files when it finishes up the installation. Saving a copy of the installer to wherever is a great idea, but to be safe you should do that before installing.
Well the full downloaded avast installation file isn’t one of them it remains after the installation is complete.
But if it is a program update from the interface, then as far as I’m aware it only updates the changed components, so no installation/setup file as such.