copy a file in a window to a different on the other window

[Michel Mélice]

It frequently happens that I must substitute the content of a file named "file1" located in a window (source or target) with the content of ANOTHER file named "file2" located in the ANOTHER window.
The only way I found is:

select file1
F5
renaming file1 by file2
OK

I would be interested by a special copy command allowing to perform the operation by just selecting file2 in its window.