I discovered another place to try entering the commands shown on the Electrum support page:  the "Console" window of the Electrum program.   So I saved the unsigned tx file in the same folder in which the Electrum program was installed and I copied-and-pasted the "cat unsigned.txn | electrum signtransaction - > signed.txn" command into the console window.   It responded "SyntaxError: invalid syntax."   

Was that the right place to enter the command?