&AtClient and &AtServer in File mode

Hi!

I have just understood the difference between client and server parts of the Script, but what if I use File mode version of 1C:Enterprise? Will it all be executed at client?

It will be execute from local (client) computer. Your computer is client and server at the same time.

In short, the File mode has a server still, so your procedures will stay at client and at server, but those client and server will both be your PC. This means that they will share file paths for example, so you should test your solution at a separate 1C:Eterprise server to make sure that you have not forgotten to pass files from client to server for processing