In the elder days of MS-DOS you would type

copy CON: file.txt

and then you'd type in the file contents, ending with enter, ^Z, enter. That would generate the End Of File signal, ending the text entry. Isn't it what the author of the documentation tried to tell - that you need to send EOF to the target device if you want it to send the data?
I think, in C, closing the stream (e.g. fclose(fp); or close(fp); ) automatically sends EOF?